It's like this. Say you have five builds. Build A is 100% effective. It is the best and it pounds things to sand in a heartbeat. Build B is 99% effective. It also pounds things into sand in a heartbeat. Builds C, D an F are 90% effective. All three still pound things into sand in a heartbeat.
Well, I might be mistaken here, but from what I saw so far there is no build say for the DH that comes 90% as efficient as Mara. Thats an example and maybe and exception to your rule. If its the case then too bad for DHs I guess, but its a good example as for what I can't understand that hasn't been "fixed".
Honestly I really doubt your "there are at least 3 builds 90% as efficient as the best build". But maybe you're right, I'm not playing the game enough to have any credibility as you might have to be honest. But the thing is, when you look at certain runes for skills, a lot of them are just plain useless or almost if compared to their most used runes, and that I can't understand 2 years + after launch.
I'm pretty sure Blizz can draw evidence of skills that are so unused at maxed level character, they don't need to try and buff 'em to reach the top 10% used builds, but ... at least give them a chance ffs
Maybe they just put to much skills available to chose from into the game...