Why refusing customization is a fallacy

[Sandpark]

The problem is that everyone can play each job. If everyone can be the same all the time, it's no specialization.
If players could only level one tank, one healer, one caster, one ranged physical and one melee, you could say that each job is a specialization of a role.

I want customization same as you. But I want mine on classes which are not are built for specialization but horizontal gameplay.

If I buy a 1969 Gibson Les Paul and 200 others do, while 100,000 buy a Fender Stratocaster. My Les Paul is still has a signature build and sound. It still has specialization, same concept with jobs. Sure you can add different strings or pickups or have it made out of different wood. But that would only change the tone, not the core of what it is.