Which superpowered Universe is the most fair?

[Reddish Mage]

Well.. of course.. its in theory everyone can learn to use Haki, though there is no guarantee how good they can get either. The same way, everyone can open a lawbook and study jura, but not everyone can get good enough to pass the tests for becoming a lawyer.

Also becoming a lawyer requires formal training from an accredited institution in most places before you are even allowed to sit for the test. An exclusive state-sanctioned board determines who can and cannot be a lawyer, and they include a lot of rules that exclude certain people (such as people convicted of certain crimes).

Law, as well as other highly regulated professions like medicine, are exactly the sort of example of something that would be unfair.

Also, lawyers don’t all pick from the same menu, certain law enforcement, military, and intelligence regulations and guidelines may be secret. Also, some places keep certain other laws or forms of law secret (i.e. Japan keeps judicial decisions secret from the general public).

That would be okay, if the characters can still choose between these classes. Than they'd block other powers at least by their own choice.

That could be away, to make it fair and still let the have the characters individual powers. Everyone can follow all the paths, but they can't learn stuff from all the paths.

Its the players that get to choose characters and character classes. The characters don’t necessarily have such opportunities. However stories where everyone is a player are a possibility. I mentioned this before, an MMO anime might fit, except they are all Shōnen and so all have secret powers and super-talented protagonists.

The very nature of these sorts of game world is to fill it with a bunch of rare and unique items and opportunities that are going to be exclusive.

Nothing mentioned is even remotely close to fitting the bill. To say something like Marvel is the most fair or even Hunter x Hunter is comparing something absurdly unequal to other things absurdly unequal to a very very big set. I’m not seeing the recognition that we’re dealing with the distribution of powers that are birthed in stories of special people who can do impossible things. One of the most common reasons also have to do with biology and inherited powers.

You can decide one universe is more fair compared to another, but to say one story is the fairest of all of them...if you then cite a popular anime or recent comic....I think you are looking at the wrong place.