Let me take this point by point (and see if I can use a forum formatting I've yet to try) (edit it didnt work and I cba trying to fix it):
1: The idea that 'what if someone doesn't have the right spells' immediately falls apart when you consider that people go into content as not-job when they're of the level to get their job upgrade
2: The current patch is 'real' because that's the way the playerbase has decided the game works. Look how many people go into, say, P4S now that P8S is the 'current raid'. It's some, yes, but a tiny fraction compared to 8. Furthermore, as Ty pointed out, there's a massive amount of non-max level content that BLU is arbitrarily locked out of as it stands. Just opening up Eureka for them would give a massive wealth of content, where they could learn so many skills all at once, helping to solve issue 1.
3: There's actually a lot of stuff you can do in WOW, and like here a lot is optional (thank god we don't have AP grind this time). I could go yell YES CHEF at the Tuskaar Soup Cooking event for rep, but I don't because I just don't feel like doing the grind. Besides, many people already ARE at the point of 'reclear raids, log off for the week' and that's apparently completely fine by SE's standards because it's still the same sub money coming in.
4: BLU pretty much already is a '2min rotation' class, with a 1min miniburst. Even in it's limited state it conforms to the meta, looking at the kit I have active atm, the only things that don't are Glass Dance and Triple Trident. But Phantom Flurry, Nightbloom/Both Ends, J-Kick/Quasar, Supranakra, Titan/Ramuh, Peculiar Light, Offguard, Matra Magic are all 1/2min CDs, and Garuda/Ifrit and Rose of Destruction are 30s so they line up too
Last point gets to be special outside of the list, it depends on how they were to implement it. Way I'd do it is to have 'unlimited BLU' be the synced, and ironically actually 'limited' version, where every spell is essentially categorized based on it's effect, and function as 'skill glamours'. eg all the cones are collectable reskins of the basic 'cone skill' you'd get from the questline (or levelling), which solves both the 'what if they dont have the right skills' issue, and keeps the only identity BLU's ever truly had, that of 'you learn enemy skills'. 'Limited BLU' would remain, also ironically, as the Unsync (and Carnivale) version, where it's limits are actually removed. This mode would add additional effects to each skill, based on it's original form we have now, such as LVL Death also applying instantkill or Petrify turning things to stone.
Additionally, I'd make it so that raidbosses do NOT have any immunities to instantkill. This means that, once an expansion is over and done with and not 'relevant' anymore (since the instakill effect only works while unsync), you can instakill the raidboss with BLU, making it way easier to re-obtain old glamour pieces, even solo, which might help address the issue of 'no space in dresser'. If it's possible to re-obtain that chestpiece from Eden's Verse by doing a process of 'run in, instakill Shiva, repeat up to 8 times' instead of having to rely on PF to know what they're doing, people might be a bit more open to the idea of throwing out some old junk that is in the 'well i probably wont use it but it's a bitch to re-get it' category. And BLU can still be used in 'challenge run, as it was back then, min ilvl no echo' kind of stuff, because the instakill effect is unsync only
It'd also fill a niche that does not yet exist: the 'support heavy, trash personal-dps caster', the DNC of Casters as it were. Or, given what I'd do to Offguard and Peculiar Light, maybe more accurate to call it the NIN of Casters.
Sorry BLU tangent, TLDR SE decided they wanted to do X with a fan favorite class and refuse to budge on it for any reason whatsoever