You basically built your Job, certain spell combos gave you certain traits when equipped together. So you basically had to balance your spell points (it was more of a point buy spell system then slots) and selection of spells between traits you wanted and Damage and utility and some method of MP refresh/healing (be it HP, regen or status ailment removal spells). With your 1hour ability Azure Lore, allowing you to access a NM level spellbook of learned spells. From a Behemoth's Thunderbolt a Vampire's Bloodrake or even Mighty Guard which is much more closer to the turbo buff it was in prior FF entries. On top of more frequent cooldowns that allowed you to synergize with your weaponskills with your spells to perform skill chains which is basically a elemental aspected explosive reaction to the elemental aspect of your chosen weaponskill and chosen enhanced spell that results in lowered parameters to the target (which traditionally a BLM or Dark Arts SCH would exploit to Magic Burst a Black Magic nuke) and skillchains had 3 levels (4 if you have the school of Legendary Weapons that enabled tier 4 Skillchains, but there are other equally powerful Legendary weapons that offer other bonuses for example BLU would ideally want their Mythic Weapon the Tizona for it's MP Drain properties or for their Mythic Weaponskill Expacion's Aftermath effect to help with TP generation which means you can deal a lot of damage by performing weaponskills back to back).
Coupled with the fact that BLU is one of the few Jobs that could essentially access lvl 3 skillchains (on their own and within their own kit and without requiring a Legendary Weapon for their Job. Meaning they also have really flexible subjob choices so you can really fine tune whatever build you think you might need/have access to, where as only SAM, DNC and 2Handed Damage dealing Jobs which usually subjob SAM for it's skillchain support Job Abilities) which otehrwise usually require coordination with other players or Trust NPCs, some of which have AI to capitalize on any skillchains you "open" (meaning you go first in performing a WS) so that they can "close" (meaning they go second in performing a WS) with a appropriate response weaponskill, though most of the time you coordinate beforehand with other players or read up on a Trust NPC's weaponskill elements/AI behaviors so that they can "open" and you can "close".
BLU's flexibility in XI with XI's game design really felt rewarding to me which is why while I can appreciate XIV's BLU, it's just not the same (this is due to the design of the game), but I also know it has it's fans as well so the best I can hope for is that they are allowed in prior open zone Expansion content (Eureka, Bozja) and even Deep Dungeon but make them ineligible for the Necromancer title and give them a meme but fun hearted title. And maybe down the line have a toggle-able more "on rails" BLU (so a curated experience essentially for any of the 3 roles that's more integrated into the DF instead of how siloed off it currently is) that would unlock as you progressed in your spell book by a % completed parameter or some such. But that would require a lot of Dev resources so i understand why something like that isn't exactly possible either. But maybe the best they can do is add another limited Job with that kind of support made for it (that maybe BLU's could also tag along on).