Ginjirou is mostly good, but if you bump his strength or speed to max he actually gets less good. I have beaten the game with him, because his non-magic move set is boss, but again, too much strength or speed and his powers lose some of their luster.
With Han, the main problem is that his moves don't hit many times, and if you buff his strength all the way they also push enemies so far back on each hit that he can't get as many hits or combo effectively, though he can sure clear a big space when the enemy doesn't bother to block. Han's secondary problem is that he really only has one spell: fire. You can buff his Intelligence a lot but it only really helps for that one spell, so it feels like wasted points. With Han you just have to be a careful player and rely on an aggressive Undead Hero to get your back. But when you have the Undead Hero on auto you end up losing out on some EXP as he carries more of the combat load, and you can also miss some alternate stages, paths, and even endings because the Undead Hero may kill something you wanted to bypass or end a battle too quickly when the path you want requires you to time out a particular waiting period.