It feels to me that this game cannot strike a good balance for grinding. In short, I feel that, as a midcore player, there is nothing much to do in this game because achievements and rewards are either gated behind insane grinds that take hundreds, if not thousands, of hours to complete (such as the pterodactyl mount from Ishgard or the mentor roulette mount), or they are just one-and-done content, where once you do it for the first time you've really done it forever, like the Lone Hero title or the MSQ (inb4 "you can do the MSQ multiple times to appreciate the lore" when 99% of players don't do the MSQ twice for fun)
Most of the one-and-done content that takes significant amount of time are actually interesting, like solo deep dungeons, Ultimate fights, and so on. But grinds that require you to do something X amount of times feel horrible in this game. They are so far out of reach that most players have no motivation to ever even try grinding for those rewards.
The problem is that there are no significant or good rewards for milestones, and that for some achievements, there are too few milestones, with most of the milestones having horrible or irrelevant rewards (like 20 achievement points) that it is functionally a single achievement with a super grindy milestone at the end with all of the middle parts being useless.
What other MMOs like Lost Ark have done better is to sprinkle many more rewards and many more milestones throughout your journey. In the above screenshot, one of the game's collectibles, masterpieces, is a long-term grind that takes roughly the same amount of time as - I would say - 500 A-rank hunts. But the reward structure is significantly better because it gives you relevant rewards along the way. You are getting a relevant reward every 3 or 4 days and feel motivated to continue grinding the collectible.
FF14's reward structure for achievements needs to do this.
---------------------------------
Beyond that, FF14's achievements are also extremely monotonic. They have you do the exact same thing thousands to hundreds of thousands of times, with very little variation. Grinding out an achievement in FF14 feels like torture. In Lost Ark, collectibles have you do all kinds of different activities, which makes the grind much more bearable and interesting even though it also totals to hundreds of hours. But it's spread apart over months and staggered so that you're doing a little bit of each every day, and for most activities you are spending 5-20 minutes on it each time, tops. That makes the grind much more bearable.
In FF14, the game does not stagger the activities for you, and does not have systems in place that allow you to switch between different grinds/activities naturally and easily. For example, if you want to grind out Eureka light, you had better stay in a party and grind +6 mobs for hours in a row because that is the most efficient way of grinding it out.
The monotonic nature of grinds in FF14 is horrible especially now that jobs and systems like crafting have been so gutted that it's even more mindless tedium than before.
---------------------------------
Finally, too many grinds in FF14 just feel flat out too insane. Grinds like 2000 mentor roulettes or 500k Skyward points on every single profession just shouldn't be a thing in a modern MMO in 2022. In Lost Ark only one such instance exists - Isle of Yearning - and that is already a huge source of consternation for players. The game needs to encourage you to do a variety of activities and try out a bit of everything. Not have you tunnel on one single activity to grind it out. That's what Lost Ark does better and is what FF14 should learn from. You do so by making sure that any single grind where you are doing a single activity lasts for a few hours at maximum. A grind that is most efficient when the player sits there for 12 hours in a row, multiple days in a row, is bad game design, period. Stagger the activities somehow, even if it means putting timegates. That's why Savage lockouts exist, so that players aren't grinding out the same encounter again and again for days to get all their loot. If it works well for Savage, it should be a thing in all other forms of grinding.