ff14 has a lot of limitations currently that are really in need of fixing as they are, or starting to become long term issues that are holding it back.
This is the top 10 in no particular order, since some will obviously be more important to different people
Available dev funding and resources: SE is being really stingy with ff14. It absolutely prints money yet SE denied the funding to bring on new severs until they literally started cracking at the seams when 5.0 launched. SE knew it would be popular, but did nothing. Each patch the servers are more overloaded and have queue times to get in. Dev resources too are insufficient- they are getting enough to keep the game ticking, but they aren't getting the time or people needed to fix the spaghetti code in places where its still around.
Cheating, rmt and botting: going hand in hand with dev resources, the devs aren't bothering or are unable to address the masses of bots being used. The rmt taskforce seems to be nonexistant now given they are advertising constantly in PF
Dev communication: It is well known by this point the forums are screaming into the void 99% of the time. The devs need to take on ideas and feedback, especially the feedback they don't want to hear like with healers and tanks
Job kits: Healers in the worst state they've ever been with redunant healing, minimum damage tools. Tanks not far behind with almost useless defensive abilities. Dps are base breaking at best. Ranged and raise taxes need removal, the gap between dps and none dps is too wide this expansion (tanks/healers take forever to do the duties) the kits are designed around balance and not fun. Homogenisation has been excessive and unneccessary. Devs need to stop dumbing down things and instead raise the weaker jobs. Include a proper, mandatory tutorial as well. Buffs and debuffs need to be readded and need to be long and strong enough so a notable difference can be seen and felt without 3rd party tools
I could rant about job kits all day and so could many others, so lets continue
Casual-Hardcore gap and difficulty: This expansion is, without a doubt, the easiest expansion by far. On one hand there are people who actively refuse to use their job's full kit (cryo mage, 'pure' healers etc)
and can get away with it. Yet we have savage and ultimate especially in NA more excluding than ever of anybody who doesn't have high parses and prior experience, and full of people who willingly fail mechanics in order to get their parse higher to the detriment of others parses. Not to mention the exclusion of ps4 players who can't parse and pc players who dont want to break the tos.
The msq and normal df content needs the difficulty bar raising and a proper tutorial implemented so there are less clueless starting players and max level players are unable to play without using their full kit. Parsers need to be blocked and an in game recruitment for statics instead of through reddit, discord etc.
You didn't need the parsers and other 3rd party tools in the coil people, and gordias was rushed for HW release and left there due to relic delays.
Also, crafting/gathering accessibility has leaned too far in the other direction, now its too easy to get into, markets have been flooded.
Housing: need I say more?
Glamour and gear: no Long hair, clipping, endless buttcapes and pauldrons, lack of variation for casters/healers so they are sutck with robes and coats constantly, gear/gender restrictions, dye restrictions, out of date models, lack of body variance (flat butt, lack of bust, no muscle on most races), poor customisation especially in the face (clones everywhere!), genderlocked races... is it any wonder the modding community has hit it off so well?
Content and release of it: Limited time content (ishgard), non repeatable content in abundance, relics are starting at 2.5 instead of 5.05 like originally thereby losing portions of the playerbase at a time. The patch cycle has become stale with ilvl being calculated. BLU being advertised as solo and ends up requiring a party and a static in order to gets its achievments, mount and even decent spells. Most of its spells are clones and meh potency and been balanced around party play. Lots of party play content despite the msq being primarily solo and no solo content other than relic. Lots of small content that dies off with no popularity or replayability like verminion, ocean fishing etc Eureka has a whole host of issues, getting older raid glam gear is nigh on impossible sometimes as you need a party still.
Technical faults: Ghosting mudras, Sch myriad issues, data issues in the glamour dresser and retainer summons, semi random lag spikes, effect failures (tank mount explosions don't show up for a lot of people)