So in your words, average players (500-750) are not good enough to play against OKW, because some self proclaimed RTS expert egomaniacs approve the current state of balance and furiously believe that it shouldn't be changed?
That is a big problem right there.
Do you know how the winrates for the factions actually look like?
Brace isn't retreat, it's an invincibility button. Why don't Pak guns or Leigs have retreat? Why don't all factions defensive bunkers, base bunkers, base buildings or own emplacement like the OKW Flak emplacement or Flak HQ have brace?
Why is there no brace for the UKF FRP if the 'retreat' is so vital?
All you need is practice to figure out how to fire stuka so more shells will hit.
At most they will bring it to half health, and one of them is going to be absorbed by brace. And even then the british player can repair it faster than 2 stukas can damage it.
Maybe give them another upgrade? Like either 2 flamethrowers or the ability to lay mines, maybe a wirecutter(but no minesweeper, they're penals after all OpieOP)
I think we really can go in any direction with them.