There are many things where some classes outperform others. Some things are just not unified.
One example is the AP useage. Some classes run out of AP very quickly while others pretty much never run out of it. I have never seen a WE or WH running out of AP, even if they start the fight with only 25% AP. Some classes have AP drain, others have not. Some classes have heal debuffs, others not (e.g. Engi). And so forth.