I'm an ardent defender of ARR's game design.
ARR always had the best dungeon design in the entire game, and frankly anyone who disagrees might as well praise Final Fantasy XIII level design.

I'll concede that the removal of some of the boss mechanics in the MSQ dungeons from ARR were unnecessary. But Copperbell only benefitted from the redesign. The layout is literally the same as before. They focused on changing the bosses.
The boss design in that dungeon was horrendous. Duty Support is not engaging, but a boss where the whole party spends 2/3 of the time waiting to take any action and a boss that involves waiting for the weak adds to slowly make their way to you only to die in 3 seconds each are even less engaging. Boss fights where half the party just stands around waiting are trash.
Even the last boss was trash. Or rather became trash, because for the past 2~3 expansions you never had to bother dealing with its original mechanic unless your party had miraculously bad dps.