Somehow Yaks had no limits on their engine operations and thus, in AH they get their "WEP equivallent performance" 100% of the time.
I wonder if it really were the Yaks or the Russians that had no limits on engine operation.
It is question of operation. Even Merlin can operate at 100% just it severely limits its resource, same for most engine.
AFAIR ASh-82 (La-5/La-7s engine) was actually certified to operate on 100% without shortening its resource.
I'll give you an example. Russian operated P-40s with Alison engine, especially early models/periods the engine "died" after about 35 to 50 hours instead of rated 120. Why? Russians pushed it to the limits and it begin to disintegrate early. I assume they did similar with Yaks.
They tried to squeeze the best they can from limited platforms, P-40C had flown without wing mounted .30 cals, only two cowl mounted .50 cals. This way they reduced weight and improved roll. P-40E was flown with 4x.50 cal instead of 6. (P-39s were flown without wing guns as well).
This way they can keep them flying when rest of the allies considered them outdated.
(Source: memories of Golodnikov 7 kill ace that had flown: I-16, Hurricane, P-40s, P-39s, Yak-1/7/9 for 2nd GIAP)
BTW, in AH if you fly Yak-3 100% all the time your range is significantly reduced. I almost never fly Yak-1 at 100% at transition times, only at climbout and combat.