Even then, you can spawn most contested HNMs these days, which is why there's nothing wrong with a Pop system. The only requirement is doing a KSNM 99 (arena fight) against an equivillent version of the HNM and you get the pop item to pop the world spawn version.

It's a pretty win-win situation as you're doing a lot of content that flows together, this is the one thing XI did well, whether you liked it or not due to personal reasons aside, not many MMOs flowed their content together well, for example doing missions unlocked end-game areas and doing quests or certain NMs unlocked the ability to progress further in certain dungeons to other content.

XI's content had very long life spans and not always because of "low drops" (only Salvage had very low drop rates), because there's always someone new or returning that needed to do x content and the gear is still worthwhile, which again, is personal preference if you like or hated that system. It wasn't until Level 80+ (2010) did they embrace the "make everything prior worthless/do this till next update" system that's so popular in MMOs.

I still yet to see the cons to allowing NM/HNM's being popped, let alone a stagger system so you can raise your chances at getting what you wanted, like Ifrit, breaking the spikes is basically the same concept as a stagger system from XI, it influences a certain aspect of the battle.

No different.