Blue Mage: Are you kidding me!?

[Seraphor]

You're talking as if the literal only way to make BLU be unique is to push these limitations onto them.

Meanwhile, there's actually a TON of design space available to make BLU a completely distinct and wholly unique class, you know, without restricting them from being able to participate in like 90% of the game's content and not even be particularly unique in the 10% of the content they CAN actually do...

Like, as a "Normal" class, they could still push leveling into the Overworld (Such as restricting duty finder until level 50/60/70/80 or something).

They could still push the Learning spells mechanic in lieu of Class Quests (Maybe they could have put in class quests that basically say "Go learn X core spell everyone would ask you to have in order to do group content").

They could still create new and different progression systems to use.

You really can't have these 'different unique progression systems' for 'normal' jobs, not if people want to "main" it.
Imagine a new patch or expansion comes out. Everyone else gets to rush through the MSQ and unlock all their skills along the way. Meanwhile you have to spend x hours hunting down your skills before you can even start the new content, or have to take regular 'breaks' out from the MSQ to go and find your skills. BLU would be held back in comparison to all other.

As for balance in this respect, you can't make BLU too OP because then it'll be required for high end raids and world first, and hold everyone back as they wait for the Blue Mages to catch up and get their skills. So you nerf them down in line with everyone else, and now BLU has this disadvantage of having to learn their skills manually while no other job does, and they don't gain anything for that.

The only way to make learning the skills manually 'fun' and to give the system any merit is to make that the goal in and of itself. By making it a 'normal' job and a viable high end raid job, learning skills instead becomes an unnecessary hurdle to the "real" goal of raiding.

Well just looking through the data mine having a balanced blu seems rather easy, use the skills they already are putting in, have a checklist you need to make with those skills (i.e, need 1 cone 130 attack, 1 aoe centered on you ect) then tune some of the skills that seem more "OP" to have reasonable numbers.

From the skillset we've got, I don't see how this would work at all.
You have Aquabreath and the thunder cone AoE that interact with each other, so they're useless on their own.
Rams and Dragons Voices, that's a combo, so you can't take those separately.
Then all of the other 'similar abilities', how do you decide which ones to take? You don't, the meta will invariably decide for you and you'll be booted for taking the 'wrong' skill, unless the skills have no discernible difference, and then what's the point?

There's no sense in 'tuning down' skills either, because then BLU would fail to work as a solo class. It'll need those massive DPS boosts to kill things that you'd otherwise need a party for. Mighty guard would need to make you as tanky as, well, a tank, but taking that into a raid as a DPS would break the mechanics. Self-destruct and Final Sting, depending on their costs/repercussion, can either be too OP or too debilitating for serious team play, with no middle ground.

The only place I see a 'separate skill set' working is for PvP. Making yet another skill set for instances... well that's just throwing a whole other job in there for them to try and balance.