Enrage timers are a worthless and lazy way to design content in any game. Either I can kill the mob with my group, or I can't. Why should it matter how long it takes me to accomplish my goal? Dead is dead.
I'm from EQ2 and that mechanic, while it does exist on some of the higher end content, is used as an obvious timer mechanic and doesn't just wipe you but starts ramping up the difficulty while leaving you a chance if you start executing well.
Enrage timers shouldn't exist in any fashion - they aren't fun, they aren't challenging and they bring nothing to the event. Pure Dev Lazy.
Enrage timers exist so fights can't be solo'd or done with completely terrible players who afk auto attack or push 1 button. Do you really want to see everyone and their mom decked out in the best raid gear possible because you don't need to be good to get it?
Following mechanics may still be hard for them but pushing as much damage as possible while still avoiding mechanics is what makes PvE hard and seperates the 'Okay' from the 'Good' players.