What do you think Akuma needs? Legit asking. I love him as a character and have a lot of lab time on him, but in a game who's meta is based around a touch into a guess into stun, hyper low life and stun characters struggle. Karin and Cammy get by (I don't think Cammy is as good as the sort of general opinion of her.. but she's still strong) on tools.. Karin has one of the best neutrals in the game with quite good range on her normals and some trickery with her rekkas and pressure, several ways to gap close and she can output a ton of damage and stun very quickly. Great walk speed and mobility in general. Cammy has dumb pressure and crazy mobility. Long range normals and best or second best (I don't know if Vega is faster?), Really solid damage and terrifying tick throw game. So they make up for low life with mobility and range and damage.. I don't list Oki and post-kd pressure because, honestly, fucking everyone had Oki and post KD pressure. It's a thing that any relevant character has in spades. Some characters have it in excess,like Laura, but almost everyone is good in this regard.
Akuma though.. I don't know. On paper he seems to have everything.. his normals are short-ish but he can fish a little with FP. His damage is quite good, he has a decent fireball and a good jump with demons being useful in a number of ways.. lots of tools and options and ways to pick and choose how he ends and behind his offense, f+FP is sexy. Pretty damn good + frames on a lot of his stuff and on and on.
Is it purely lack of mobility that holds him back? When I play Karin I feel like I can poke and peck and try to engage and then back out when it doesn't work right, but on Akuma I feel like I really have to commit more and once I'm in (which can be tricky) if I can't make it work I don't have an easy time of escaping and trying to reset the situation.