I think in the end its very simple: We know FFXIV devs are spread too thin. There are direct statements, and evidence looking at sub-systems of the game forgotten and left dying for sometimes more than a year.
We also know the implementation of the first limited Job was an unmitigated disaster, BLU is basically dead content, bug-ridden and has little to no repeatable gameplay value. You touch it once for a few days, push it to max, and are done with it.
Then we see all those other sub-systems that are not updated anymore, and dead in the water: Mahjong, Verminion, Chocobo Races for the Saucer, then we have Fishing lacking its lvl 80 gameplay, PvP recently being all but deactivated and generally not working well, Squadron gameplay, Grand Company rewards and ranks, Housing having major issues (though its not dead really, I ll admit that), Guildhests and of course BLU.

To add to that, content pace has slowed down for dungeons, almost all new content is now released in a permanently outdated gear range, and aside from the MHW crossover and the ultimate fights once in a blue moon, there has been no new concept or subsystem added for max-level gameplay beyond the typical content rotation of 4 raidbosses every 6-7 months.

In light of these critical shortages, the thought of adding yet another subsystem that cannot be maintained and will be impossible to keep relevant sounds like a truly, truly bad idea to those who would rather have one or more of the OTHER shortages being adressed.

HOWEVER: I am always happy to have new classes. I think the WoW Hunter in the olden days had a good idea of a class that tames beasts, but ultimately they are pretty similar to each other, mostly cosmetics and one special ability. That way balancing is easier, and collectors can still run around looking for that rare spawn with the unique color.