Ranged DPS role is about to be excluded from all content

[SaberMaxwell]

I'll be taking an interesting mechanic: UWU Ifrit's nails.

This is a bad example, mainly because it highlights Physical Ranged's strength at being able to continue their rotation throughout a baiting mechanic like Ifrit's Nails with relative safety. TL;DR of this post is your point that Phys Ranged have to keep their rotation going while Casters don't is incorrect, and the fact is that they do need to keep their rotations going which means they need to understand their mobility options as a Caster very thoroughly and plan accordingly, and even then they need to take gigantic risks to just not get caught by eruptions.

A better way to tackle it might be the amount of mechanics a Phys Ranged is expected to handle: in UCoB, they're the designated fire baiter no matter what. In both Twin and Adds phases. In UWU, they're one of the designated eruption baits, as stated, but they're designated for every set of eruptions, whereas the caster usually bows out after the first mandated eruption bait for them. Summoners at the time, who had the mobility of casters, could keep going however. Phys Ranged are also expected in many parties to take a Thermal High from Garuda all the way to Ultima, and to eat one of Garuda's attacks away from the party and then navigate their way back to said party.

The responsability will obviously be on the ranged as first and a healer/caster.
The non-physical ranged will only have to worry about their own aoe and the nails, you can cast before but I highly doubt you can cast during the mechanic apart with instants.

You highlight this as though it's a boon for a caster to not be able to cast during this. In the first case, you're wrong: every second casters aren't casting, they're losing substantial levels of DPS, so yes, they'll be keeping up a rotation through this phase, but they need to be slidecasting / instant casting as much as they can through it; this also means they need to have an intimate knowledge of their slidecasting threshold and they need a large amount of foreplanning to maximize the use of their instant casts. As an example, there is a strat specific to Red Mages, where the Red Mage will melee down a nail by themselves so they can enter Redoublement > Verfinisher during this phase. Even while doing this, I found myself needing to tempt death to hit the last slidecast needed to keep 100% uptime through here.

The physical ranged, however, needs to keep up its rotation and dps, that's an extra layer of difficulty and must be rewarded not punished because you are the job for... the job.

Which leads me here. As a Red Mage, you're no less expected to keep up your rotation, doing so is just much more dangerous. In keeping my rotation going through careful allocations of instant casts and slidecasting, I am still keeping my rotation going; I never did UWU on the other casters, but I'm sure Summoners had their methods and kept their rotations going, and Black Mages probably had to stock their Triple+Swift for that same baiting mechanic. It's just significantly more risky to do so. Not doing so, however, is a gigantic loss in damage for Red Mage, both in current damage output (no DoTs, no autos, no damage going out every second that a damage spell isn't landing) and in future output, as not casting means no mana generation, which delays and hurts melee combos going forward through the fight, and in long fights like UWU mistakes like that can cascade.