All Howitzer based units
Static howitzers are destroyed too easily by cheap call-ins and all howitzers, even the moving ones, are upstaged by their rocket artillery equivalents. They should have more AT utility through stunning or crits to better define them against the rockets.
I personally never liked howitzer emplacements, since there is a range limitation )exacerbated in larger maps), and the need to micromanage the popcap, manpower and builders to access it. Compared with off-map stuff and mobile artillery like Katyushas, they aren't particularly powerful unless it's firing at a sim city (which means only one faction).
I personally preferred if it was like how they designed the British base howitzers: based in HQ sector, has their own range limit, but you have units that can make them fire beyond range. Make it so the spotting unit needs to maintain target for the howitzers to keep firing: you risk a unit for the howitzers to fire, and if the opponent fails to take it out, they will continue being shelled. Off-map abilities by comparison cost munitions and CP, and are "blind fire" barrages.
Advanced Vehicle Crews
Made for an extremely niche purpose, that is prett much unused by USF. Needs a complete overhaul or replacement.
I would have at least made this ability where repair units can repair faster but with certain penalties, like increased manpower upkeep while repairing, and/or Vehicle Crews can already use critical repair and gain vet faster or something. An SMG weapon upgrade on the second-worse squad in the game, topping only medics, clearly showed Relic ran out of ideas.
Assault Engineers
Good when they come out, but bad durability scaling means they rarely last long in a game thanks to their need to be so close to the enemy to be effective. Should receive another man at vet 2 or 3.
A bit ambivalent on this one, they're clearly meant to deal with specific threats. Maybe if they got Sturmpionier's Minesweeper package upgrade that boosts repair speed and can swap minesweeper, and the 5th guy comes in at vet2 like RETs?
I&R Pathfinders
Dedicated scouts and artillery unit, that is neither good at scouting or calling in artillery. Needs to be able to camo when moving in cover and artillery range should be increased.
I forgot: do I&F Pathfinders have autosnipe like Jaegers? Do the Airborne variant still has them? At three men, there isn't any good reason to remove it, even given the arty strike.
M8 Greyhound
A terrible light vehicle that can't even take on a 222 despite similar role and being more expensive. Needs some general buffs as well as coming stock with sideskirts as this is a redundant upgrade that everyone uses anyway, and hurts an already munitions heavy commander.
I actually think Greyhound's 37mm gun should be a non-doc upgrade for the M20, and of course having their armour buffed a bit. What the commander ability has instead is a more generalist unlock that gives multiple units the shrapnel shell ability: the Sherman's 75mm gun for example had the T30 canister shell in real life; even the 90mm gun for Jackson had the M336 canister shell, though that might be OP since it is a tank destroyer. Keeping it to Stuart, Greyhound and Sherman seems sufficient to make it a potent ability for players confronting infantry trying to go for a snare.
Recon Sweep
Redundant thanks to majors recon which does the same thing for cheaper. Doesn't even provide consistent vision to support indirect units. Should be replaced with loiter.
Indeed the very least it should be a loiter, otherwise it is literally an off-map version of what the Major provides.
Airdropped Combat Group
Overly expensive for a late game infantry call-in. AT gun should be removed since it is a liability for using this ability behind enemy lines like it should and inflates the cost too much. Para types should also be consistent as well.
Problem with this ability alongside I&R Pathfinders is that they're obviously designed to be used in conjunction (what with the landing beacons); removing one kind of negates the other, though frankly neither are particularly great anyways. I assume the best method is to replace it with some sort of airdropped ability, maybe a version of UKF's airdrop ability where medical supplies and 1x bazooka and BAR? Lowering its CP would also make the commander a more attractive option while not turning it into some Paratrooper clone.
WC51
Decent unit but heavily overpriced. More expensive then a 222 in manpower and fuel.
Can't really comment on this unit since I don't use it much, but one idea that came to mind is ability to toggle to allow it to have 360 degree HMG capability? Maybe add suppression when it is toggled? At least then you got a fragile vehicle but one that can lock down parts of the map at the cost of being a mobile taxi like it should. This might end up just replacing Fighting Position, though.
Another idea is that it uses the repair upgrade ability described below, turning this little cab into the vehicle version of ambulance, this makes it supremely useful even in lategame where it provides repairs for vehicles. Upgrading removes transport and/or machine gun.
A third idea is that it can also be upgraded to work like Opel truck. The result is a light vehicle that while a bit expensive compared to 222, has many utility options to support your other units, either by repairing or providing extra resources. Both ideas seem remotely faithful to the Mechanized theme.
M3 Half-Track Assault Group
Because who doesn't want 2 0cp level units at cp3. Just a terribly weak ability that is never used, should be replaced with a M5 or M5 with assault engis.
In Ardennes Assault, M3s could upgrade to toggle a repair aura for nearby vehicles, I think this should have been the option, especially since the AA variant wasn't scrapped from the campaign or anything. Or even just give it same quad ability, I mean the M5 was really just a beefed up M3 built for export, plus Relic just gave USF the same M5 through the Calliope commander anyways. Really, the solutions for this unit is not only simple, but already exist.
Paradrop Crew Weapons
I'm still not quite sure why this wasn't like it's coh1 equivalent. While some use it to get around teching limitations, at least one of the abilities will be useless. Should simply drop with a 3 man squad to crew it so it can actually be used to reinforce the front quickly.
I never really liked the coh variant, it would allow playesr to drop a suppression/ AT option right behind an enemy for an off-map ambush. And given the way CoH2 works where you can "blind drop", this means it is that much more OP. I don't see these abilities as useless.
If we really need it, then I say a suitable compromise is that you need to drop them within landing beacon range for them to come manned, which means pathfinders need to have laid them down strategically. This also has the added side benefit of the beacons also providing reinforcements for the paratrooper guys that drop with the weapon.
Foward Observation Post
Because who doesn't want to pay manpower and fuel to access full priced, mediocre abilities within a limited range... Abilities should be discounted due to the initial price and limitations of the ability.
I think it also lets you use the abilities separately, despite the text implying they have shared cooldown among them. Before I got the commander I assumed that the abilities were free, but shared cooldown and long cooldown time. This way the maximum range can be expanded and you have the dilemma of scout plane but no bombers, or use an existing unit to scout and try for an airstrike.
Instead what we have is a massive munitions sink that lacks range. It's like buying a 90mm AA emplacement for home defense: badass sure, but you'll NEVER use it.
M-42 45mm AT gun
A weak unit that is useless the moment the first medium comes on the field. Needs more utility either through some sort of stunning or snaring mechanic or giving it some AI utility.
I'm thinking they come with a toggle option to use AP shells, which is how they work now, and canister shells, where they are more effective against infantry, and more so if closer range, and have a special ability similar to Tread Shot at vet1. This doesn't replace your regular HMGs or AT guns in any way, but greatly enhance them when used in conjunction. Unlike Button, the vet1 ability could be something like blinding the target vehicle, but it can otherwise move normally, or it temporarily immobilizes them like how the Gammon bomb works.
Assault Grenadiers
Similar problem as assault engis with bad scaling. Could just generally use better vet bonuses to keep up with allied infantry.
I was thinking that maybe giving them some AT ability that is unlocked once you research Battle Phase 3 or 4, where they aren't deadly against light vehicles in the early game, but remain viable as part of the Grenadier meta once you start getting StuGs or Panthers. The ability could be a simple one like the same Grenadier Panzerfaust, or even 1x panzerschreck upgrade, making them work a bit like Stormtroopers.
Another idea is just give them an upgrade that offers 2x flamers and demolitions, mimicking the cut Urban Assault PGrens unit call-in.
Trench
To easily turned on you by the enemy, thus rarely used. Should be identical with brit trenches.
I thought about this before, I think one solution (if at all possible), is that slit trenches are owned depending on who owns the sector: if you build it in friendly territory, the enemy can't take it; however if the enemy neutralized the sector, anyone can take it; once captured by the enemy, you cannot use them. Being free and rather fragile, this doesn't sound terribly OP. But whether this is actually possible given the game engine and such I dunno.