The ‘population issue’ is not only about the overall player numbers, it is about the number of players available to the matchmaker at any given time for the set BR range (which seeks +/- 1.0 BR for assembling the matches).
Two modes, CA and TO, would put greater demand on the MM to fill parallel BRs (say RB GFs 4.0 and RB TO 4.0…and it gets more complicated if one mode is preferred over the other). As Gaijin is very sensitive about queue times (especially in yesteryears), they may react adversely to queue times doubling even when that doubling is not an issue (a la an increase from 30 to 60 seconds).
Beyond the problem of ‘flat spots’ where the matchmaker has difficulty assembling matches due to other reasons (unpopular range, heavily favored mode, etc), the real issue around population based on history would be less the population at hand and more Gaijin’s reaction to it.
Queue time anxiety has been a big factor in why Gaijin has compressed BRs in the past…and that obviously has its own ramifications. “Population issues” could well come up (I’d say they’d be largely minor and scattered), but the real issue would likely be the latter…Gaijin’s reaction.
The ‘population issue’ framing is shorthand for all of this.
Putting aside the imbalance of 9.X+ (the top tiers of the game have always featured balance issues due to technology creep), there are few reports of ‘broken’ CAS (ex. the Yak-9K).
Outside of top tier, almost all posts complaining about CAS are complaints about defeats dealt by enemy CAS–not anything being ‘broken’ or functionally inaccurate about how the enemy aircraft is doing what it’s done. Obviously, an enemy vehicle defeating a person doesn’t mean that enemy unit is broken…it just means the enemy was successful in defeating them.
Having played RB GFs extensively from 1.0 to 9.X, I cannot say I’ve seen any serious “CAS problem” to discuss. The Yak-9K’s flight model is bogus right now and it needs fixing…but that’s about it (it’s still entirely vulnerable to enemy fire too.)
The real issue with balance (air, ground and overall) starts at/beyond 9.X as technology gets emphasized over player experience and skill. At that level and above, modules matter more and more as stock syndrome becomes increasingly painful. That is where the lion’s share of legitimate CAS complaints originate: top tier is a mess.