Originally Posted by
Shurrikhan
The effect of this is less (unique) than one might think.
The difference between the cost of uptime lost to a DoT-user and anyone else is, in essence, just the lower potency-per-execute of its otherwise high-ppe DoTs; the investment cost of its earlier GCDs. That said, the likes of a long combo would be just as negatively impacted. A boss jumping away into a CS just before RA-Atonementx3, Vorpal Thrust, or Gnashing Fang would be just as painful due to those GCDs being similar "back-loaded" in their GCDs invested.
That being said, they could always change the bosses from being invulnerable even to server-tick-based damage to merely invulnerable to wholly new damage events.
Tl;dr: Brief periods of boss invulnerability are not a sufficient reason to remove DoTs from the game.