Eddiek:
The problem with the Yak9U is like this. The La5 is much faster than any of the Finnish/LW planes under 10k or so where most fighting occurs. But it can be outturned by the BF109G2/G6 so there is some balance.
The Yak9T can outurn the 109Gs, but is just a touch slower and does not accel as well so again there is balance.
So with these two planes in the set it's possible for all the majors have some advantage even in mixed fights but still maintain balance.
But if you add the Yak9U it breaks the balance. It can outrun, outurn, outaccelerarte all the 109s and 190s and it never runs out of "WEP" like performance. And thats the problem - it is the class of the G10, P51D, D9, and LA7.
And balance is what made the FinRus setups so popular in the past.