Last night I was in a P-51d and tried to fight a 109K at around 12k ft. After winning the merge (the K-4 pilot didn't expect me to fight, I think) his La-7 countryman climbed up into our fight and forced me to extend. I laughed out loud watching that La-7 try to catch me at 12k ft. 
The La-7 is only good at extremely low altitudes, so that's another reason why it doesn't deserve a perk.
One, while the La-7's performance doesn't *dominate* at 12K, but it doesn't exactly suck either. Check DokGonzo's for yourself Anax. The La-7 does not give up a huge amount in speed to the P-51 at 12K-20K, is as good or better in climb, and of course still has a much lighter wing-loading.
Two, most fighting in the MA is low, the La-7 has no reason to leave its comfort zone to hunt, and, finding itself in trouble, easily re-enters its comfort zone by diving. If there was as much, or indeed any combat above 20K the La-7 might not have inordinate value relative other fighters, but such is not the case.
Oh, and if we unperk the SpitXIV, then not only will we have the La-7 making the deck basically an untenable place for the high-speed E fighters to be, the unperked SpitXIVs running around will have the same effect at higher altitudes. If making the P-51s, Jugs, 190s, Typhoons, etc., obsolete in the MA sounds like a good thing to you, well then, I'm afraid we must part ways on that one.