I gave the Yak-7B a try in the Late War MA last night. I found the rockets to be only marginally effective, requiring a direct hit for a kill. Not easy to get direct hits... Still managed to get 3 kills and a couple of assists against a swarm of tanks. When the swarm continued, with fighters arriving to pick the "bomb tards", I grabbed an F6F instead. Kill a few tanks, then embarrass a few fighter jocks. Rearm and kill some more... That, along with several friendlies and dr7 sitting in the enemy spawn... They quit.
The Yak-7B has very limited capability. I believe that the Yak-9T is more effective against ground targets, and with the much lighter 20mm gun option, more capable than the -7B air to air. Indeed, the P-40N is a much better all around fighter-bomber than the Yak-7B. I'll fly it because I like the challenge, but if you really need to kill stuff, 95% of the plane set is more effective, including the Ki-43.