If what you say is true, why I don't see JT, KT on "pro" games? because if If go to sc2 for instance I can play with all units, with your thinking you will have only 2k people playing this game, if this game were in a good balance state, lest say 85-90% then this game will have thousands of people playing it, how many people have installed this game only to uninstall it due to lack of balance and bugs, why age of empires have more players? I can and play age 2 right now I won't see this disastrous game breaking "skill plays" this game is played because it is unique and there are other like but by any chance it is even 50% balanced.
With that mindset, the same things happen in both SC2 and AoE2.
JT or KT are either non optimal choices or niche, focused to be mainly used in teamgames. Pro games are been played in their majority in 1v1 in a curated map pool, with counter faction picking been a possibility.
How many pro game have u seen in SC2 which are based on teamgames? Same can be said around AoE (which is a bit more similar to CoH2 with teamgame tournaments vs 1v1 ratio).
SC2
Terran: i think it's the most well rounded though the Thor might be a little too good in the Zerg match up. We rarely see nukes been used and Ravens feels more like only been built once every so few games at all. Worst than that is banshees, cloaked ones which have a shorter window of opportunity than an M3 clowncar.
At least Reapers are been built so often even though they become irrelevant past the first few minutes of the game.
Zerg: "Can't believe there are tournaments on this game. I can't believe that with all the game breaking unbalance this game has"
Let me mention pre nerf and removal of infected marines + infected growth and swarm host + nydus combo or just turtling into brood lord meta.
When a caster GM/Master main zerg you tells u "It's surprising how zerg was able to lose at all before the nerfs" i don't think you can put SC2 in such a high pedestal.
As far as useless or niche things go, we have Microbial shroud and Swarm hosts now. Infestor enable the kinda bad Ultras, though they are mostly only viable through having such an overwhelming map + eco presence that u are essentially taking bad trades but having so much bank that you choke down the enemy who is in fewer bases.
Toss: i'm surprised you don't cry about Toss design, which i would argue has been the cheese + deathball army since day 1.
While everyone can cheese, there's been specific metas on which the race has only been viable if winning through cheese and mid game all ins.
I think it's almost as well rounded as Terran, though there's a discrepancy between Pros vs anyone lower than Diamond regarding Air armies on the lategame.
AoE2 DE: because i don't want another page of words, i'll simply say that if you have issues with commander balance or units been niche, i don't know what game have you been playing by not seeing the glaring issues there are with Civilizations dominating on specific maps or plenty of unique units not seeing the light.
There's a good reason picks and bans are used in tournaments so we don't see the same civs every single time.
Number of players: not many games in ANY genre can achieve what CoH2 has done in actually increasing it's player base post release + maintaining it's number through so many years, specially without direct support from it's developers.
AoE2 DE has it's numbers because they finally were able to make people abandon voobly to a functioning remaster compared to the badly implemented AoE2 HD.
SC is a monster of it's own and have it's cult behind it.
As much as many people have fond memories of CoH1 and look back through rose tinted glasses, i would like to compare this situation with old Battlefields. Yes, 1942 and BF2 were good for a small niche playerbase who was extremely dedicated to it. But once you try break out of the small pond, you will start to find that not everything look as good as you think it was.