I agree that you have to re-balance caster spells when removing this terrible interrupt mechanic. But it would still be for the better.

Most of these points are invalid though. BLM's would still be interrupted by actual interrupts, knockbacks, stuns, other CC. Not to mention they can't just stand there and get beat on and expect to live. While evading and LOSing they can't cast either. They might get one or 2 casts off while "tanking" as a BLM, but they're going to die quickly just being a target.

"There would be randoms who just mash their stun skill making DR kick in." - this though... How do you think BLM's feel when randoms just mash buttons breaking their CC?