Why is Akali allowed to be viable top lane?

Because she isn't at all viable in mid.

She has always been Mid/Top so why are you complaining that she still is viable in both

She should be nerfed, agreed.

Mid lane Akali is trash. Top lane Akali if you go AD bruiser build is good enough to maybe winning the game.

Don't ask questions like this or Riot might seriously start locking champions to lanes. Akali is a viable toplaner because people are having success playing her top. Don't use terms like "allow" or you'll encourage Riot to enforce play styles.

The same reason why Lucian is?

Cast off midlaner who can't compete with the current strong picks there. That's why Ryze was seen top or Viktor.

It is known that everything that might get washed up from mid, ends up top. As some other users already stated. There are other cases where there might be a niche fluke to play them there, but usually, it's a high elo insight (with insight i mean that the player understands favorable match-ups with each champion they play). The 'insight' niche might be copied later on by a few lowbies that will only follow the bread crumbs.

I don't think she's problematic though. I'd rather play against than as literally ANY champ top.