The core identity of BLU is collection, as would be the core of all "limited jobs". Beastmaster collects pets (think pokemon in the overworld) and puppetmaster (some sort of crafting mechanic to create mammets?). We aren't talking about combat, we are talking about the primary activity of the job, which is building up a library that can be used.
I have not actually disputed any of your complaints btw, I acknowledge that the actual spells of BLU aren't that interesting, and what the player can do with those spells is limited (I believe that squadrons and roulettes should be something that BLU should gain access to), but the idea of lumping BLU with all other jobs in terms of level cap and access to raids/pvp/deep dungeon does a disservice to the potential that the content has.
Reading this makes me dismiss a lot of what you have said, unfortunately, which is a shame because some of your ideas are good and resonate with my own opinions. Please read again what I said about BLU raiding. I don't want BLU to participate in traditional raiding, because the game mechanics there do not suit BLU. What I want is for limited jobs to have their own endgame, or "raid", which is currently the masked carnival (which I love, but also admit has some flaws, such as being exploitable and needing more longevity), where mechanics unique to limited jobs can be implemented, and we can get an endgame far broader than what the cookie cutter raids of normal jobs are able to provide. Once we have a second job, I feel that this idea can be expanded upon a lot more.
I agree on principle that elemental skills should be expanded, but I am unsure as to how this could be achieved. The masked carnival works because it is a BLU only bubble where the game can work completely differently, whereas the rest of the game is shared between BLU and normal jobs.
While this is true for the most part, it is just a mentality that you have. You don't know the roadmap that the devs have for limited jobs, and they may be a direct response to the comments that the traditional formula is stale. It may be an attempt to create a parallel experience that provides something completely different. All we know from the devs end is that they said that other limited jobs are being planned, which tells us the scope of their vision. Think of it like crafting and gathering, are they just pieces of side content that the devs have to funnel resources into, or are they parallel experiences to the battle content that some players dedicate their entire game experience to?
How long do dungeons and raids take to consume? What do you do once you have beaten them once? Again, I have acknowledged that BLU is a bit too limited, and does need some changes to give it more longevity, but that doesn't take away from the idea of a limited job at its core, only that BLU needs some QoL to give it more things to do (such as squadrons and older roulettes). The normal job system has had 6 years of QoL improvements, whereas BLU has had a single (arguably meant for testing the new system) patch. We don't know what the dev has planned for BLU in 5.0, and we don't know what they have planned for limited jobs in general. Maybe you are right and we get absolutely nothing and this is all that the devs planned for limited jobs, but I find it hard to believe that the devs would create an entirely new classification of job and not want to expand on that idea in the near future.