That doesn't actually make sense, though. Like I said, at level 99, Fire IV #6 is also too strong to justify skipping, and, yet, it is no stronger than Fire IVs #1 through 5. If you've got two mutually contradictory complaints about something your actual problem is probably a third thing, to whit:
That's quite a big "provided" you've slipped in there! Obviously, cutting astral fire short after having cast Blizz4 to stock up on umbral hearts was a problem. But, additionally, cutting a non-standard setup short was also a problem. Like, if you did all the weird transpose+mana tick required to expurgate some combination of B3, B4, and whatever else from your rotation, entered AF3 with just enough time and MP to cast F4-F4-F4-Despair... but the could only cast F4-F4 before a boss mechanic forced you to move, you had to cut your intended fire cycle short and lose damage! Ahhh, the non standard setup is so rigid, it forces you to cast as many F4s as possible (which was 3 or 4 or something, I forget the numbers) or else it's suboptimal, I can't stand it.
The actual thing that's changed is that BLM's transition and resource-stockpiling spells are no longer skippable. But it was never actually good to fail to cast as many F4s as you possibly could given your AF3 start conditions. You always lost damage unless you squeezed every last cast you could out of your MP and elemental gauge.
I'm sympathetic to this and I'd actually be fine if it still required the full complement of six to cast; my biggest priority is just removing the extra gauge, which I feel like only serves to clutter my HUD. We could have each umbral heart replace itself with an astral heart, and then each astral heart start glowing and crackling with power as it transforms into an astral soul, or something like that.