They need to return to FF11's design where you are one member in a party of adventurers just to fight same level mobs in the overworld. Final Fantasy is a JRPG and JRPGs are about parties, not one man alone. FF11 was pretty much classic adventuring NES/SNES Final Fantasy but you control one character in the party. The problem with FF14 is that you solo the game. You yravel the overworld alone, do quests alone, do FATEs alone never needing to actually group up and communicate it's just an everyman for himself zerg like in GW2 and WoW. You can now do dungeons alone, and LFG where you get automatically matched with randoms who you will never see again is not a fulfilling experience. You only ever need other people to do the 8 man trials but again LFG is not a substitute for the classic FF11 experience where you literally could not solo past level 10 and had to party to continue, and you had a limited pool of people on the server who were at the same leg of their journey as you so you got to know them and make friends.

Leave the 500+ hour long visual novel to actual singleplayer games. Don't try to paste it onto what is supposrd to be a mulyiplayer experience.

The next FF MMO need to improve its faction system. Having players be a part of different factions gets them more invested into their character and what is going on and interacting with their team. Faction warfare and fighting over control of zones is also an amazing motivator.

Character customization needs to be brought back, be it equipping subjobs or mixing and matching different weapons or spells, etc.

Move away from the holy trinity, go back to FF11 where you have buffers and debuffers and CCers and thieves who grab extra loot and mages who teleport and stealth the party and pullers, etc.