Light vehicles (such as the Stuart & T70) over performing
USF Mortar over performing
Lack of viable commanders for Soviet & Wehrmacht
Wehrmacht infantry not scaling in late game
Wehrmacht's lack of counters to light vehicles
Soviet Penals over performing
Soviet Guards Rifle over performing
Other
Hmm, so the real question is which six problems do we want to have ignored?
Best bet is to get the one thing changed that has the most impact.
Light vehicles over performing seems to suggest more attention to allied LVs. I don't know if this means to include the 222 or not. Changes to T70s, Stuarts, AEC, 222s, and Luchs would all have to be different. The issues with each aren't universal.
USF mortar is probably the biggest glaring issue that shouldn't exist in the first place. What it is, I don't even.
Wehrmachts lack of counters to light vehicles is pretty much the same as light vehicles overperforming.
Wehrmachts infantry not scaling to late game relates heavily towards their lack of counters to light vehicles, as well as the USF mortar wiping them, as well as Soviet infantry having early game synergy.
Soviet Penals over performing has to do with synergy with Soviet Guards synergizing (Strong AT, pocket AT). Without the other they don't really overperform.
"Lack of viable commanders for Soviet and Wehrmacht" is a very confusing. Either they're hoping it means the players want them to build more DLC, or to fix the multitude of obviously terrible commanders. Hopefully it means the latter, but commanders relate to an issue with COH2's whole design, not balance.
Light vehicles play, the USF mortar, and soviet infantry have large impacts on Wehrmacht's infantry play, and therefore their ability to last to the late game.
I
feel like given the options, that "Wehrmacht infantry not scaling into the lategame" could potentially have the biggest impact on all the related issues. Or rather, all of these seem to contribute to Wehrmacht's (infantry) failing to get to (and surviving) the late game.
However, based on reality, the USF mortar, which shouldn't have existed in the first place, and especially not in the ridiculous form it is in, is probably the biggest glaring issue. But coming up with a method for Wehrmacht infantry to scale better into the lategame might have the most beneficial impact.
So, if there's actually going to be changes that are tested and balanced, I'd say wehrmacht lategame. If it's more 'what couple of numerical values do you want one person to change once randomly without testing in the next couple of months and never revisit?" then I'd go with USF mortar.