I think one problem you'll run into is people consistently running down the timers in the hopes that their preferred gear piece gets rolled on first.

I personally prefer having max melee sized AoEs because it offers yet another means of skill differentiation from other melee players. I don't think that fights need to be designed with 100% uptime conditions either, because that's why we're given movement tools in the first place. I'm not really sure why the discussion around the current tier's hitbox size is at all relevant here, and as a tank you're always going to be the first person to be denied uptime if space around the boss becomes more limited. This design benefits you much, much more than it benefits melee dps. We could always go back to 'spin the dice over which tank gets the downtime flare marker' if you prefer.