Why refusing customization is a fallacy

[Gilthas]

As OP said if you are not raiding it won't matter, when you DF it wont matter you will just continue the dungeon.

Let me repost this:

Having unbalanced jobs is bad for everyone. It's bad for the player that likes the job because he gets shunned from most parties, and it's bad for those who don't play the job, because they get stuck with an underperforming job in duties.

The argument that all jobs play the same is also pretty much a fallacy. Even if you're of the opinion that the current jobs in each role play the same (I disagree) adding specs won't change that, it'll just add more jobs that play the same.

[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.

[Delily]

It's not a fallacy because every time a game has customizations, the vast majority of players go with the optimal build. There are years of data that proves this. The other not to do this is that adds the yak shaving of spec balancing. The devs spend time right now balancing skills between jobs, and now you want them to do the same between specs.