I've been looking in on this thread from time to time and I see people moving to positions where you can't really have a coherent discussion because people are disagreeing at fundamental points you need to reach an understanding on to even start talking.
Here's my example: D&D has three pillars of play that are described by the designers. This means that during a session you'll find yourself, broadly, in three different modes of play. I don't understand how it's anything but a given that each class would have something do do when each of those pillars comes to the front. Some classes will be better than others, but each class will be able to contribute something based on what they are.
The biggest problem with this is that the exploration and social pillars aren't really explained in the same detail as combat, so there isn't enough depth to them to design for it. There are third party products that expand on exploration, and from what I've read they do give each class something to do.
Design core products, call them Robilar's Pillars of the Game, or something similar, and create class features so a fighter might be a good quartermaster, or be on the lookout for threats in a social situation, and you'd avoid this issue. Having time in the session where a class has nothing to contribute, outside of things anyone can do regardless of class, makes those classes seem worthless in them. And it bores players. But if we don't even see it as a problem that the fighter is drifting off or acting up during the King's Ball, the discussion might as well not take place because all we're going to do is talk past each other and make the poor mods' days tough by getting snarky.