I like the way you're thinking here. I'm all for that kind of tweak to GB. Dropping it completely seems wholly unnecessary.

Overdrive needs something to make it more lucrative. I'd rather they just remove the penalty entirely, or at least make Overdrive apply some sort of debuff to the target(s) after use to more than compensate for the DPS lost.

I've always felt that an ability with the name "Wildfire" implied a fire raging out of control, not just a delayed explosion. I wouldn't mind a DoT mechanic added to WF, but your Cooldown idea sounds great, too. I'd rather they not bring back Lead Shot. I missed it at first, but now that we have so many other new abilities, I don't really want even more to throw in my rotation.