if you want BLU unlimited it's need to fit in the same desing as the other jobs, 20-30 skills for everything, dungeons, raids, trials, openworld, you can't leave BLU walking around being the broken job with his fancy op skills for everything except roulettes, raids and trials, and it's against BLU lore lose spells every expansion to get new ones, thats the price for being a unlimited job and its against what make BLU a blue mage, watching monsters doing attacks and i can't learn it memes all day.
if you want to keep learning more and more spells all of then should be limited and locked in to masked carnival, witch lore wise dont make sense a all.
you say it at the other way or something? other jobs learn most skills by just leveling up and SE make every job learn his new skills by level except the last one this expansion to mitigate this problem too, we asked to SE to add more restrictions on dungeons to avoid that (mostly ilvl restricition and jobs only on dungeons starting from lvl 30), the restriction of acces dutys without certain job quest is something that has the done a long time ago i agree, but again BLU will have a lot of problems bcs it will be frustrating if BLU learn limited spells and real combat spells in the same way and maps.
that last part was aiming to the future but BLU right now is better tank that PLD and WAR in ARR, mighty guard, diamondback and bad breath offer such protection that BLU can solo tank anything they want in a party, white wind is the most powerfull healing spell in the game, he can top the entire party in a question of seconds, big raid aoe? everyone use diamondback then white wind, problem solved, for stuff like this is why i understand why BLU is out of duty finder and roulettes and i belive BLU should never be on the same level of the other jobs with the current desing since can break the 2 tank 2 healers 4 dps composition or exploid some group mechanics with skills like this.