Gaijin have been adding ARM’s to planes quite selectively, some planes received their ARM’s, some didn’t due to some balance reasons. Though one plane doesn’t really follow this logic - its a Su-39.
Su-25T also received ARM’s, but Kh-58 is a sidegrade to Kh-29T at best so nothing is wrong here.
But Su-39 for some reason gets much better Kh-31 and Kh-25MPU’s. While Kh-31’s are still a sidegrade to Kh-29T with its old seeker, Kh-25MPU is whole different story. Not only it comes with all-band seeker and IOG - most importantly it replaces Kh-25ML’s, not Kh-29T. Its a straight up upgrade in terms of anti SPAA capabilities while remaining on same B.r as Su-25T.
Nothing to do with balance reasons. This is just the first batch of ARM’s coming, not enough time to add them all in one go, on top of all the other content for the update.
More will follow in future Major Updates.
Situational ARM’s aren’t the gamechanger you seem to think they are. They’re pretty neat, but nothing that’s really going to affect BR’s in practice.
Gaijin claims they cant give the tornado Gr1 ALARMS, even in limited quantity because it will have to go up in br, i dont see why the su39 should be exempt from that line of thought