You seem to be unaware that Yang is actually more capable than any of your party members when it comes to withstanding attacks. You may feel that Yang loses a lot of HP when he is attacked. But I've heard that he actually was able to withstand the blast from a cannon with enough firepower to wipe out an entire kingdom. Yeah, supposedly Yang just jumped in front of it and took the blast. It's weird because they say he lived through it, and recently developments have shown that he's still in fine condition to enter physical combat. You'd think that if the cannonfire didn't kill him, it would at least incapacitate him to the point where he was no longer able to fight.