To add on to that, look at all the complaints they’ve made about rare mobs being too hard this expansion, and those take less time to kill and do fewer things than the world boss.
So why is this a problem when it’s not problematic for a system like M+ to have 20 different difficulties with their own rewards, or for a game like Horizon zero dawn to effectively have 12 difficulties (6 for each of NG and NG+).