So you can only do content if you have the time to grind for a set of gear for each content, if you don't have the time you are, by all intents and purposes locked out. Good idea, lets lock out the majority of the playerbase from most of the content and see how long subs stay at the present rate.
Or what about those who play multiple jobs? Raid leader, oh we down a tank today, Sapphic, you have a geared tank, would ya mind? sure, Ive got the ilvl but dont have the exact gear needed as Ive been only able to get the gear for monk, so we can progress. Can you wait a month while I grind the gear so we can run the content tonight?
DF queues would get worse, as atm it is pretty easy to gear up a secondary job, aka tank that some, myself included, like to run content with other jobs. With your idea players would only be able to focus on their main job/role farming all these difference sets for each piece of content.
And you think it's a good idea? lol.
I don't care what FFXI did or didn't do, it is irrelevant, Why do you think players are playing FFXIV and NOT FFXI?
Bad idea is bad.