Mastery is different per spec. It all depends on what it does, you will never see the same percentage between two specs as its effects are unique to every spec. I'll be spreadsheeting this weekend most likely, to get the best we can from people.
Also we did ask Bagel never forced, we questioned Hyams as well and he said no so we didn't push it. We will always look to get the best we can, but if you don't enjoy the spec you won't play it to its potential so its a waste of time swapping. You just start to hate the game.
But fucking hell what have they done to warlocks.