Why refusing customization is a fallacy

[Reynhart]

Let me repost this:

You can repost it all you want, it's still a lie.
Since "underperforming" is "compared to something else", you could frequently say that one job is "underperforming".

Back in 2.4, MNK and NIN were better single-target DPS than DRG, so, in a way, every DRG was "underperforming". SMN and BRD were lesser ranged DPS than BLM, so they were still "underperforming".
Back in 2.0, WAR was a lot more weaker than PLD. So, he was "underperforming"...but to the point where clearing content was significantly harder as a WAR. That was a balance problem.

Now, DRG is a better single target DPS than MNK or NIN, etc...

People will still play the job they like, because it's fun, no matter how they perform, as long as they can clear the content. You obviously exagerate my idea by supposing one spec performing waaaay better than the other.

Sorry but your wording was bad, I read it wrong. You are aware that there already is a certain degree of customisation in place, e.g. a Scholar who focuses on healing will want to prioritise Crit, a Scholar who focuses on DPS prioritises Det and Accuracy

Actually, yes, there is a certain degree of customisation...and it's pretty much only tied to Arcanist. If SCH can focus much on DPS, it's because its class is a DPS one so it has a fair DPS potential.
I really think job branching is an interesting concept, and adding that to other classes would be a first step on customization.