Akuma was only actually banned in US SSF2T, which I don't think means much anymore because I doubt anyone still plays the non-HDR version at a competitive level (he's not banned in HDR, of course). In Japan he was soft-banned, meaning it was implied that using him was lame and dumb, but not actually against the rules.
Either way, there was a legit reason for banning Akuma: he broke the game on a technical level. No character in SSF2T had any sort of counter for an air-to-ground projectile because no character except Akuma (a secret character most players didn't even know about at the time and who required an arcane button input to access) had one, so if he was properly allowed it probably would've ended up like SSBM's NO ITEMS FOX ONLY FINAL DESTINATION. Whereas there are mechanisms in place in Pokémon to not make sleep assrapingly good (abilities like Insomnia, for example), but no one pays attention to them because the Pokémon with those abilities aren't viable or there are better abilities available.
No, I don't play Smash Bros. (nothing to do with tournament play, I just don't like the games all that much), so I don't even know which version you're talking about or what those things are. That series isn't exactly known for being well-balanced, though (see above), so it's not surprising that things would be banned.
A good multiplayer game should be balanced well enough that you shouldn't need to ban anything, even if some concepts or characters are more or less viable than others (disregarding games that can be easily patched for rebalancing). Having to ban entire classes of moves (OHKOs and evasion boosts) and severely limit other parts of the game (sleep, freezing, number of unique Pokémon on a single team) are clear signs that it's not anywhere near a "good" multiplayer game.
Also, as an example of a game I do play where things are banned in advanced play, Magic: the Gathering has a sizable list of cards that are banned from tournament play or restricted to a certain number per deck. However, the ban list doesn't affect 99% of current players because most of the fully-banned cards are stupid rare and haven't been in print for well over a decade.