They've had heavy losses, that's absolutely a given, and why they partially mobilized and used prisoners but if it was in the numbers given by a totally not biased american source while Zelenskiy is in Washington right now, then the Ukrainians would be in Crimea by now. 90% is akin to the almost total destruction of your fighting forces. Cannon fodder will never replace trained professional soldiers and if you lose 90% of the latter you simply lose the ability to mount coordinated military operations in any meaningful sense, you collapse and ultimately sue for peace. You're done. That's my opinion anyway.
War propaganda is always about minimizing your own losses and exaggerating the enemy's. I'm all for helping Ukraine and stand on their side but I'm not willing to give into this blind cheerleading and believing numbers coming right from Disneyland.