So, some fun facts:
-Mighty Guard gives BLU the highest self-buffed attack speed in the game before even considering DW5 as a possibility (sort of tied with DNC if the DNC subs something stupid like WHM).
-Due to the nature of Mighty Guard's buffs, BLU now has higher DEF than a PLD and higher MDB than a RUN at the same time.
-The Regen, coupled with Regeneration, gives BLU nearly the single most potent self inflicted Regen in the game. Regen 5 is only slightly better, and Embrava makes SCH still much better at it, but still.
Verve, possibly the MDef- one that no one has yet, is the only spell still worth casting under the UL umbrella.
Harden Shell would require either an enormous potency buff or an enormous duration buff, or both, to be worthwhile.
Pyric Bulwark would need to work like Third Eye or something similar.
Thunderbolt may have an application or two, but Shock Squall or Temporal Pulse would serve the same purpose.
Droning Whirlwind is technically useful, but there are no realistic applications.
Blistering Roar can like... get you out of animation lock or something. Yay.
Bloodrake may still be applicable if you really need an emergency heal and are willing to forgo the myriad benefits of Mighty Guard, which especially when cast on an entire party heavily outweigh 2-3k HP.
Tourbillion... well, it's nice that it finally works, but that extra 8% DEF down that isn't even fulltimable is not as meaningful as what MG affords defensively or offensively.
Gates of Hades was outright replaced by Searing Tempest.
Bilgestorm doesn't last long enough to be of worth, especially now that Tourbillion works. The defensive benefits are not nearly as potent as Mighty Guard's.
Absolute Terror is absolute trash. Was useful for a few Delve NMs when it first came out.
Crashing Thunder and Polar Roar may as well not even exist. They're flavor spells only.
Uproot may have some extremely niche use somewhere, but it still probably doesn't outweigh the benefits of MG.
Honestly this could all be changed if SE implemented a charge system on UL. 1 Charge every 90 seconds or something (some spells would need to be adjusted as to not upset the balance further, but small price to pay for more options). MP cost and cast delay of these spells already pays for most of them.
At the end of the day though, I embrace our new Mighty Guard overlords. It's an incredible spell that other jobs would kill to have.