This discussion is about homogenisation, yes. There's another term that we use to describe 'homogenising' the total DPS output of jobs (read: equalizing) across a given role. It's called job balance. Having some jobs that are only valuable in progression is a terrible design decision. Every job should provide value in progression. Every job should provide value in optimised clears. The current design promotes a different type of homogeneity, in which every group locks in PCT into the caster slot.
Healers aren't individually taxed for having access to raise. That's because it's a property of the role. Nobody looks at a healer raise and sees this as unique job flavour, either. If raise was standardised, then there is no longer any need for a raise tax. You can instead look to other forms of utility as a means of job diversity. We currently have job with a personal barrier, a raidwide barrier, a raidwide heal, and burst mobility, without any form of utility tax whatsoever. It's clear that the DPS discrepancy within Casters specifically is about raise and nothing else. So standardising raise as a role action frees up jobs to diversify their utility in other ways. By your own admission, we see variation in utility between melee jobs with a much tighter DPS balance than you see on ranged. Why else would there be such a large DPS discrepancy amongst ranged jobs?
There are a couple of ways to implement Raise as a role action without tying in a MP cost. If I were designing a 'Phoenix Down' action, I would give the action a set number of charges that scale based off of fight difficulty (i.e. less charges on harder difficulty fights). Perhaps you could tie in a short mandatory cast that can't be made instant. You create the option of replenishing charges either on a fixed timer, or relative to pre-determined fight transitions that refresh uses, or relative to LB gauge generation. There's a lot of flexibility around how you could influence access to this.
My impression was that the whole point of experimenting with Raise design in Criterion/Criterion Savage was to try to develop novel solutions to the problem of non-healer raises. There are a lot of different directions they could go with this.