Nyzul 75 was an effective use of end-game content in a randomized dungeon. SE has done it before, I wouldn't mind them doing it again.

Nyzul 99 required an absurd amount of coordination and communication, oftentimes a certain job setup (a SCH or two and a BRD), which often promoted using third party tools to clear it with any consistency - and even then there were luck factors involved. While it was fun, I wouldn't really say it was incredibly well-designed content. This is not what SE should do outside of an Extreme-type mode.