Every game is different for everyone, but it's also true that many games don't get a fair shake by most people.
FFXI is one of those types of "games" where to give it a fair shake you have to get fairly invested in it from the outset. I've met quite a lot of people who played it up to a point back in the 75 era, never reached 75, and then put it down because they couldn't get past certain road blocks or just stopped having fun.
It's hard to admit, being someone that loved it and played it actively for over a decade, but it was far from perfect (much like the real world). Even moreso in the present day where the endgame has become a vertical progression since they introduced item level.
A lot of its systems(generally the older ones) waste your time and treat hard work unfairly, catering to those most willing to be scummy, aggressive, egotistical, and mean. I imagine that all of the people I've met over the years who quit "early" just didn't luck out like I did by finding friends and forging strong bonds with them. The kind of friends that just come PL you and shoot the ***or help you camp an NM for hours on end. We don't get those people's perspectives on XI because they leave, and once they've left there are only our voices to talk about the "game."
When a game is also a filter, anyone who gets filtered out isn't going to hold it in good esteem. People also only know as much of a game as they play, so the ones who quit before level cap raise or shortly after, of course, only want the 75 era back. It's what they knew and what they loved.
FFXI is a "game" where each iteration of its game over the years has filtered out players. This is true of any MMO, but the changes made in XI are usually so dramatic that they upheaval many people's preferred play methods each time they happen. The RNG nerf in early 04? Lotta RNGs quit. Two-handed buff in mid 2007? Lotta MNKs quit. Abyssea 2009 leveling the playing field for once, giving people strong weapons and gear for almost no effort obtainable by few people? Lotta salty head honcho LS leader types quit, because their favorite way to play was exploiting large groups of people (if they weren't already LM-17'd in the Salvage bans).
Everyone who's played FFXI has had a wildly different experience.
As far as FFXIV goes... I've got firsthand experience for 2.0 and later, but it has virtues and faults just like its predecessor. Its main virtue is that it's pick up and play. Anyone who plays the same job will be using the same skills in the same way to varying degrees of success depending on player effort and skill. There's a lot less to figure out about its mechanics. Damage values are simple. Gearing is simple. It's hardly a filter at all. There's almost no way to be exploited by other people, relative to XI. Gear always drops but has less value. Crafting is more involved and more fun. Best of all, it can actually be put down without withdrawals.
For me, and for a lot of other people who got hooked on XI, it was a "game" that couldn't be put down. The only reason I even put it down for XIV in the first place is because I had a romantic relationship in it go sour around that time, and it made me quit (and Kalila implored me to try XIV simultaneously). I couldn't bear logging in, and knowing that my ex was around doing things with my friends and brother still. Even now I still want to login, and my subscription stopped in 2019 (15 years subbed to XI). Even knowing it is different, and I don't have good gear or groups or anything anymore... even knowing having to use my brain to do just about everything gives me a headache, even for the simple stuff... I just want to go sit in Kamihr Drifts or Xarcabard [S] or Castle Zvahl Keep.
Like XIV will never be as good as XI, overall, for me. But I mean, XIV is just a game. XI is another world.