If I were going to make an MMO: Mastery
If I was making an MMO, Anyone could use any weapon, but the effectiveness would depend on how skilled a character was both, with that weapon type and also the familiarity with the specific item.
Exotic weapons or crazy enchanted/magic/legendary weapons would be difficult for the average player to just pick up and start using effectively.
A player who always uses 1 handed swords could find a magic 1-h sword and not necessarily be a master with it the first time he picks it up, but he would have a pretty good idea where to start and what to try, but if that same player finds a chain whip, or a scythe, it would be much more difficult to learn.
This could reward players who use many different weapon types by letting them pick up and learn new weapons more quickly and being more adaptable, or players who want to focus on just one weapon type by reaching higher levels of mastery with their favored (or couple) weapon type(s).
Here’s an example of how this could work: Level 1 novice finds a [Thunderfury, Blessed Blade of the Windseeker] on the ground. Lucky! He picks it up and can immediately tell that it is very strong, but he has absolutely no idea how to use it right. His low 1-h sword proficiency combined with his low familiarity with Thunderfury itself would mean that our Level 1 novice is unable to draw out any of Thunderfury’s strengths.