Mixed, or any doubles, works better when all the players can defend as well as attack, even if the actual level is not the same.
Playing doubles with 3 4.5's and one 3.5 doesn't work well. Or, in my case, 3 4.0's and one 3.0.
And I've been awestruck being the only 4.0 in doubles with 3 5.0's. That was tough to get through.