Akuma has been banned since 1994. You won't find him included in many tier lists because he's just not considered a part of the game. If someone asks me the ST top tier I say "Balrog, Vega, O.Sagat and Dhalsim". It doesn't even cross my mind to say Akuma.
This tier list for example doesn't include him.
This tier list (need Shift_JIS encoding) has Akuma's matches at 9-1 across the board, but its author, T.Akiba, is not a top-of-the-top player (although
still very strong), and is known to have some weird opinions on other matchups. For that matter it also says "仮" ("provisional"/"interim"/"without substance") next to Akuma's name, which would seem to indicate that the results are based more on common understanding than personal experience, probably because nobody has put serious time into Akuma since 1994. Notice how both of these lists allow us to identify the author(s) behind them and judge the merits of their authority, which is how you tell if a tier list is credible, rather than by if it happens to be posted on a credible-looking site.
His banning in HDR was a separate issue. The argument for banning him in HDR, where he is significantly less powerful (but still far, far more powerful than intended) was essentially "This character is
maybe not overpowered enough to be banworthy by our traditional standards, but he takes a game whose sole purpose is to be a better balanced version of ST and makes it worse balanced than ST. If he's not banned, we have to just go back and play ST anyway since the game isn't different enough from ST to stand on its own merits despite the inferior balance, and Akuma is already banned in ST anyway, so it's not like we're taking something out of the game by banning him. So we may as well just ban him and play the better game without him."
Ultimately a lot of people ended up thinking HDR was a worse game than ST for reasons unrelated to balance anyway, and to the extent that either gets played in tournaments these days (in America - ST has been going strong in Japan since forever and shows no signs of stopping) ST is the more popular game, but that's another issue.
Honestly I have my doubts if a game released these days with an ST Akuma-like character would see them banned. Players are much bigger on the "play something else" mentality these days, plus the scene is so much larger and more distributed that it's harder to get people to agree on anything. A character of HDR Akuma's power level definitely wouldn't have been banned in any other game.
I should note that I think demanding a proposed ban in Brawl live up to David Sirlin's arbitrary standard of banworthiness set by a game hardly anyone in your scene has the slightest bit of firsthand knowledge about is absolutely ridiculous, but since people are gonna do that anyway I might as well correct some of the ignorance surrounding that game. It seems like whenever this comes up most of the discussion degenerates into arguing about the true nature of ST Akuma's brokenness rather than arguing if MK matches up to Sirlin's
idea of ST Akuma's brokenness, which is really what he is saying the standard for banworthiness should be. ST Akuma
is completely busted, but even if he isn't, that just means Sirlin used a bad example; it doesn't change the fundamental nature of his argument.