It seems to me, good game designers experiment. They try four bad ideas for every good one. Being creative types, that make stuff up just to make stuff up, and follow a chain of concepts just to see where it goes. They formulate theories that get taken apart. They put stuff out there, see how it goes, learn, and try to do better the next time. Mistakes teach them more than success.
If Mike Mearls had the exact same game design goals and philosophies now as he did 7 or 12 years ago, whatever they might be, I would be afraid to trust him or his work.
Up until 4th Edition came out, the style of gameplay where players said "I want to try this" and the DM/GM/ST/whatever said whether they could or couldn't was pretty much universal.
I don't think that's true at all. Treating the rules as holy writ is a tendency within rpging that goes all the way back. In the early 70s, Gary Gygax used to be weirded out by all the letters he received asking for rules clarifications. The Sage Advice column in Dragon to answer these queries started in issue #31.Up until 4th Edition came out, the style of gameplay where players said "I want to try this" and the DM/GM/ST/whatever said whether they could or couldn't was pretty much universal.
then designed 4E