I'm just not exactly sure how much it would actually help. The game is DPS focused. While tanking/healing duties and requirements are important, you spend very little time actually doing them in comparison to your DPS contribution. For those who want those two roles to have more engaging DPS elements added to them, my mind doesn't compute why you would want healer and tank oriented members on the design team. It makes more sense if you want more tanking and healing type requirements added into gameplay. If that's what you want, then it becomes a bit of an issue because those things involve changing current encounter design.

I know if I was to put my own design team together, the team that designs battles I would definitely want them to be well rounded, and adept at all roles in the game and fully understand the fundamentals that go into all three. I would imagine that is what this dev team is comprised of as I won't even pretend to try and claim how extensively each of them play not only every role, but every job in the game.