I dont get it why people all of a sudden think a boss is weak when all the raiding content have felt the exact same way.
Guilds in vanilla did not one shot all of MC, BWL, AQ40 and there was usually 1-2 bosses guilds where stuck with for weeks.
If you increase the HP of KT why dont you increase the health of Cthun also so it require more than 1-2 weaken phases?
Also i think that the fourhorse men work good as a gate keeper in nax. if you can clear 4hm you can clear the last two bosses also for sure.