I do agree with the OP, they brought nice QoL changes and the way the content can cater to a broader audience, but they didn't even try to change anything about the gameplay inside, or improve upon it, making the core of the content another reskin of palace. It's disappointing.
The thing you're completely missing for sure is that the optional quantum boss is all but part of deep dungeon. It just happens to require clearing that deep dungeon to access, but otherwise it's just yet another regular boss that has nothing to do with deep dungeons and rogue lites.