How about a non-support ranged dps?

[RiceisNice]

I wonder if this line of thought wasn't one of the reasons which created the MCH/BRD copy paste issue.

We are limited only by the resources, development decisions and creativity. Both mechanics and jobs can be adjusted.

There are no mechanics that directly interfere with MCH/BRD's gameplay though. In the case of healers, Searing Wind/Nisi directly conflicts with being in melee range of anyone voluntarily. It's not a good example to make. BRD/MCH feel like a copy/paste job because of them both having GB/WM, as well as MCH really having no outstanding mechanics exclusive to themselves, not what they (don't) bring to the table (compared to other roles anyway).

If MCH had an actual mechanic where it involved swapping barrels to toggle between AoE, damage:TP effiency, or timing ammo usage akin to aetherflow (or really, giving more than just two skills an additional effect in form of debuffs, DoTs or self heal) and not be an objective dps increase to be used as soon as it comes off cooldown (effectively turning it into an oGCD). They can design job gimmicks/mechanics that don't actively screw them over because of boss mechanics, looking at how DRK and AST turned out.

I don't see why having a melee healer unable to do nisi or searing wind is a big deal. Isn't the whole point of the game to play multiple jobs? Not every job has to be a good choice for every encounter like how if you have a lot of movement blm is a bad choice, etc. I personally think it would be more fun to play if you had to pick and chose party composition to play optimally rather than anything working anywhere.

If the idea is "you play the job you want for the content", then sure, it's not a problem. It does become a problem if it comes to "any job can complete any content". At that point it becomes worse than what you see with PLD and AST in savage, because using your examples, a melee healer is completely useless and SoL for something like searing wind, or really any boss mechanic that discourages stacking (thunderstorms being a generic example). Not to mention most of the gear distribution actively discourages this with job-specific weapons and gear. Of course they can design future content to accommodate that, but it'd be an incredible anchor to what they can do if they have to assume the healer has to stay with someone to be able to heal them.