But that's exactly why flight has been removed. Because it's too good at doing the one thing it was never intended to be used for. And rather than design limits to flight but keep it for its intended purpose, they decided to remove it outright. Flight is equivalent to your 'rotation' in this case, your ability to function effectively. Your new rotation isn't fun, the boss was never challenging, and you still have to fight him weekly out of necessity (ie rep grind). This trickles down to other aspects of the game hurting because you've lost a fun set of abilities. The worst part about this? You can have your fun abilities back when the grindy boss is no longer relevant.
Besides, if your argument is ever going to be 'makes the content too easy', then what do you have to say about high ilvl gear making all those mobs and quests a complete cakewalk? Like I said, the repeatable content has never been challenging, so I see no reason why to 'stick with the old ways'. I could easily play devils advocate and say 'Gear ilvl should scale down because it lets you consume content too quickly.', but NOBODY wants that.