I think that the biggest thing holding CoH2 back is that balance tends to be narrowly focused with an eye to fixing whatever the current meta is without any consideration of why it is the way it is or the long-term consequences of changing it.
Take the old heavy tank meta for example. Matches used to end by who could spam Tigers/IS-2s better because both tanks outclassed anything their respective factions could field. They simply weren't designed to properly require combined arms and instead of balancing them to fit their respective factions they were limited to one per player and buffed to become super-units while the real issue with heavy tanks and CoH2's fundamental flaw went unaddressed: the game is balanced around timings and phases rather than armies and units.
This post by a very good player is a good example of what I'm talking about:
The biggest problem, for me, is the light-vech meta. The meta demands you rush out a light vech or get crushed. Why? Well, light vechs do quite a few roles:
1.) They control the battlefield - with the mobility of light vechs, they can easily zip across the battlefield and control any harassing/solo capping unit. Because this can often end up in a wiped squad for the receiving player, it's generally better to concentrate 100% of your forces to 1 area just at the threat of a light vech and to play more effeciently since that 1 capping squad will no longer be viable.
2.) They deal a lot of anti-infantry damage - this mostly pertains to the T70 and the Stuart - the luchs and AEC deal some AI damage, but are not as big as offenders as the former. Because of this, it can often be useful to keep these units on the back line and plink away with a rapid fire rate at infantry lines and deal significant damage before return fire can even be attempted by AT guns. So light vechs also act as a mobile gun platform meant to mow down infantry.
3.) Utility vs vehicles - Most light vechs have some penetrations vs other tanks - making dedicated tank destroyers like the puma even weaker vs it's intended unit to counter. As such, not only do T70, Stuart, and AEC have pretty good infantry-killing abilities, but can also go toe-to-toe with other vehicles (even medium tanks).
IMO, smart light-vech design should have their roles limited to harassing units or a fragile mobile gun (like the flak halftrack for OKW is now). They should not fill all 3 of these categories at their cost.
What does this mean?
Well, it means T70, if it wants to keep its movement, repair, and ability to help penetrate tanks, should not be dealing significant damage to infantry (something more like the AEC). It should be a unit that can eventually force off a squad, but not force an instant retreat from the other play and punish him very hard if there's not AT nearby (why solo units suck vs Allies).
Light-vechs, as they are now, are a no-brainer, anti-everything unit making them an easy choice to put into any strategy.
Additionally, they promote lazy, non-competitive gameplay as their rapid rate of fire means they can easily A-move around the field and score a lot of kills with the click of the button. This is in contrast to infantry micro, which requires smart positioning and unit pairings (i.e. Gren at long range vs conscripts) to play effectively. Light vechs like the T70 and Stuart generally dominate the field at first sight.
VindicareX is correct that light vehicles are currently a bit of a mess balance-wise but doesn't understand (or at least write about) how it got to this state. The current problem with light vehicles is that they're balanced for the mid-game light vehicle phase rather than being balanced to be a viable option all game.
What do I mean by this? Light vehicles must be overwhelmingly powerful during the light vehicle phase to justify the resources spent on teching and building them since they become obsolete late-game. This is modified by utility in a few cases (222 and UC AA, M5 and 251 field reinforcement, etc.) but the fragility of the Stuart, AEC, and T-70 mean that buying a new one during late-game is often a waste of resources. Compare this to the Puma. 50 range means that the Puma can do damage in late-game without needing to worry as much about the proliferation of enemy AT weapons.
In short, the solution to the light vehicle meta is to balance units both for their initial arrival and to give them a place in a late-game army. Infantry are already fairly balanced all game (ignoring certain weapon upgrades) but vehicles and AT weapons are generally not.
The earlier a vehicle arrives, the less health and armour it should have to make countering it easier within the early lack of options. By the same token, it should have a low target size (< current 15-18), lesser lethality, higher mobility and lower cost so tanks and AT guns don't make it completely obsolete in late-game and it doesn't dominate the mid-game.
Balancing AT weapons is similar. The later a weapon arrives, the more damage and penetration it has and the more it costs. Earlier AT weapons are more accurate and mobile to make it easier to hit but don't do enough damage to destroy a light vehicle instantly.
Picking a random example, the Ostwind should be more mobile, cheaper, and harder to hit than the Brumbarr but have slightly lowered lethality and less durability when actually hit. Currently the Ostwind is significantly less lethal than the Brumbarr and has exactly the same target size but all the other factors hold making the Ostwind generally less useful than the Brumbarr.
When units are balanced along these lines a player can choose the specific type of unit to counter an opponent's army instead of choosing whichever comes from the highest tech level. Against light vehicles you would choose light AT guns, infantry AT, and light tank destroyers (Puma, SU-76, etc.) while heavy vehicles would encourage heavy tank destroyers, AT guns, and AT emplacements to fight frontally but heavy units would have difficulty fighting a flanking force of light vehicles due to weapon and vehicle rotation, fire rates, and harder to hit targets.