You can blame players for ilvl actually. It started as gearscore, which was a player made scoring system for gear, but was horribly exploitable with healers using DPS trinkets etc to increase their gearscore to satisfy player made checks. Thats still somewhat doable with ilvl, but not to the degree gearscore had.
That said, I feel that keeping gear for an extended period of time is a bad system. Aside from social interaction, loot is more or less the main driving force of MMOs. If you release a new raid tier but no one wants the gear from it over the gear they got 2 tiers ago then what's the point. New raid tiers and new expansions are supposed to have fancy new loot as incentive for people to dive into it, with harder fights to promote the feeling of progression, which is an ever so important feeling in RPGs of all types.
You say it's a good thing if you get to keep gear because they had unique effects that kept it relevant, yet WoW did this exact thing last expansion with a certain trinket from Nighthold and people hated it. I speak of Convergence of Fates for Warriors in particular. The effect of that trinket for warriors was so strong that even despite nerfs it was still their top go to trinket for the entire expansion - and they hated it. There were so many new cool trinkets they wanted to try out and use but even by the end of the expansion warriors still wanted Nighthold runs to try to get the best version of the trinket they could get. And if they never even got the trinket they were heavily gimped for it. This was especially bad because no one wants to go back to farm old content unless they are gearing up alts or new members to be viable in the new content.
I hated gearscore back in the day. Ilvl is eh but it at least is a half decent indicator on what you'll get from the player, and it helps newer players determine what level of content they should be trying out. It's the player made scoring systems that cause all the grief, as they are often exploitable and unviable as benchmarks. Thank goodness FF14 doesn't use anything like raider.io. Logs, at the very least, aren't that well exploitable without doing stuff like stacking dancers and dragoons on one person.