Which percentiles are you using for this, out of curiosity? Because using anything above 90% or below 70% is very suspect. I checked the 70% and 80% percentiles, and PCT is ahead of VPR/SAM/MNK by... 1.3% in cdps. Sure, if you wanna nerf PCT by 1%, I guess I could see it, but 1.3% is hardly a meaningful difference.
And, regardless of where I think jobs should be in dps, let's not slap "range flexibility" on PCT and BLM. Yea, they have range... but they also have cast bars. Or should melee be penalized for "instant cast flexibility"?
It's extra funny, because M3 actually poses a lot of challenges to the caster jobs with actual cast bars. Casters have never had free uptime anyway- melee apparently just forgot that, a long time ago, they also had to work for their uptime. The difficulties melee have in M3 are the same ones that casters do. Same for M2 and M4.
I mean, you end with "It should but there's a difference between being viable and just outright better" when double caster isn't better now (not even close) and hasn't been since Stormblood. But yea, the moment double melee isn't unequivocally better, melees need to put in some elbow grease for uptime or a non-melee job is top dog, it's a "problem".
The "serious discussion" of 2x caster+2x melee being better is also not very serious. There has never been a time in XIV history where a comp without a physical ranged has been the best, and it still wouldn't happen if BLM did PCT levels of cdps (just off some napkin math I did when checking the PCT cdps percentiles in the NM raids). And even if you nerfed PCT cdps by 5% to have it behind the melee overlords of XIV, guess what? All the issues with physical ranged are still there.