Profile of Hannibal

When entering mid game, you need the P4 to keep up the pressure and fight off the Allied medium. The Command P4 has a too glaring weakness in AT to be used as the first vehicle.
Later on, Ostheer can transition into a very efficient T4 build. In smaller modes the unit forces you to concentrate into a small area while the mode rewards flanking and spreading out.

In larger modes, I find the unit to be okay. But this was still before they switched a lot of abilities within commanders, can't remember using it in the "new" commander lineup.

One issue I had was that it was always a bit hard to fit into your build population wise. Yes, it helps infantry as well, but one issue might be that first you don't really see it so you don't realize, and second the bonusses to vehicles are effectively much larger than for infantry. Given that you have 40-50 POP for vehicles and the Command P4 takes 12, you have roughly ~33 left. Since you just built a unit for pure AI use, you'd need to follow up with a Panther (-18 POP, 15 left). Giving you one other vehicle of your choice. The most effective way in that regard is to spam mediums, which is not the most effective way to play larger modes.

The utility buffs back then were quite nice. I think it is still a bit hard to fit into builds, especially since it always needs quite some micro to be on the front line, but safe from enemy tanks as well as always needing to target enemy infantry.

Since they are an smgs unit that can not really charge vs most units their main fighting role is to defend vs flanks or ambush, thus as I have posted they are combat wise useful only in specific situations.

Rifle engineer units like CE and CE can contribute mediocre even from longer ranges.

The fishing capabilities of Pioneers are exaggerated by OP.

That's not really true though.
Yes, don't charge them from max range across an open field and expect them to win. But literally all maps allow for closer range combat and have plenty of areas where you can ambush or simply manage to charge in from lower range. These are not very specific circumstances, they just work how all SMG troops work.

His complain is about the first engagement not about building extra RE so even if a RE cost 100 manpower the first engagement results wouldn't change. Talking about cost in that situation does not really make sense.

As for pioneers they are not useful in combat past minute 1 unless under very specific conditions.

Purely for the first engagements I agree with you.

The last point though is quite a hyperbole. Vanilla pioneers can contribute until enemy mainlines get either upgrades or vet2, which makes them useful in combat for at least the first 5-10 minutes depending on the matchup. Especially in smaller modes where they are not focused out as much but can go more often into 1v1 situations.

There is a flaw in "rack" system and I had pointed out years ago (in 2017) when it could had easily been fixed:
https://www.coh2.org/topic/60230/balancing-dropable-weapons

But there are also solution:
1) units having a modifier for slot weapons
2) units picking different version of weapons

To be honest I hope that CoH3 will feature some generalized "weapon skill" stat per squad that provides a modifier for weapon DPS based. Technically, this could already exist by giving each squad a separate accuracy modifier and somehow exists with different vet bonuses, but basically every unit starts out at a modifier of "1" and only vet creates differences. This is basically what you suggested back then if I understand it correctly, at least broadly categorizing units into three classes.
The current system makes base Conscripts or builder units just as effective with a picked up weapon as alleged elite troops with proper training.

The current solution was to make most weapons non-droppable and force every unit to use mostly unique weapons, so that the weapon accuracy can be tuned instead of the squad's "weapon skill".
Changing the weapon to one with different stats on pick up would solve the issue, but at the cost of high maintenance.

To circle back to topic:
I am fine with CoH2's current approach. It's not elegant, it's not optimal. But at least regarding rear echelons, it is okay. The faction works without them being potent early on. USF's issues are elsewhere, so even if we'd get another patch, I'd probably not touch echelons.

I find Grens very well balanced at the moment. I think the Gren/Conscript balance is similarly good to what I remember it to be years ago. Start the fight from long range, and your Conscripts will lose, start it mid to close and Conscripts will win.
Haven't played much Brits recently, but as OST I always had the feeling that Sections usually win against my Grens if they are in cover.

Looking at the statistics Ostheer in 1v1 has slightly below 50% winrate, which probably indicates that they are a bit too weak. It would be interesting if the winrate depends on game length and to which extend, but at least generally it is safe to say that Grens do not carry Ostheer to victory.