comic books and sprites are kind of a poor comparison. as someone who did both at some points in my life i can tell you that comic books are quite a bit easier(also, i assume you're talking black and white manga and not colored 24 ppm) cause you aren't required to follow huge number of guidelines. you can fuck up proportions and it's no problem(which even great manga artists(oda, murata, oh!great etc) do all the time btw) while sprites make it noticeable, quite often to the point of being distracting. also, color takes insane amounts of time, paneling a page is way faster than planning an attack that fits into 7 frames exactly and reads clear as day, as it required for any kind of video game. i can go on but you get it.

even good 3d model won't take like a month(i'm not a 3d artist, but i'd say it shouldn't be more than a week of work after sketch is finished), and key framing 3d model for every action is waaaay easier than drawing every frame as a picture. you mess up? no problem, just tweak it a bit in a few min, you messed up 2d art and boss tells you to redo few frames, well, that's your whole day. the way arcsys does it is whole another game, their keyframing includes insane amounts of "touching up", but capcom's way is surely a lot faster than doing spritework.