…but it literally isn’t. Mythic Kil’jaeden was a 600-1300 pull boss and is widely considered to be one of the two hardest bosses this game has ever seen, with Mythic Uu’nat being the only boss that could compare.
Mythic Fallen Avatar and Mythic SLG are two of the hardest non-endbosses we’ve had since Spine of Deathwing.
Mythic Council of Blood is one of the hardest non-endbosses/non-penultimate bosses we’ve ever had as well.
Mythic N’zoth, Mythic Azshara, Mythic G’huun, and Mythic Jaina were all extremely difficult bosses that blow most older stuff clean out of the water, each being a 250-400 pull boss.
Literally nobody thinks this game is too easy except for the players who don’t do the content they think is too easy.
PTR testing gives you literally no advantage. You have exactly one hour to do anything with the boss 99% of the time and strategies for actually-difficult bosses do not develop in under an hour. It literally exists as a means by which players can test mechanics to see if they’re actually functional.