Rather than create an imbalance, I'd rather jobs just got full combos earlier. There's absolutely no reason why a 3-ability combo with an oGCD can't be had for all melee classes by level 18.

Actually, in point of fact, I think there's enough of an imbalance already inherent in the fact that level-synced players keep all of their Role abilities. As a WHM in Sastasha at level 70, I get Esuna, Lucid Dreaming, Swiftcast, Protect, and Largesse (I'd swap one for Cleric's Stance, if I knew what dungeon I was jumping into). A level 18 WHM in that same dungeon, freshly leveled, would get either Cleric's Stance, Protect, or the ever-useless Break. That's already a healthy advantage, to say nothing of the fact that my higher-level gear essentially means I have capped base gear stats for the dungeon, which a real level 18 is less likely to have.

Could you imagine adding Aero III, Holy, and Regen on top of that? I could probably out-damage most natural level 18 DPS-role classes with those, simply based on my AoE capabilities alone - unless they nerfed them to the point where it wouldn't be worth using them.

All in all, I sympathize with the frustration, but I'd rather see job complexity increase more rapidly and be available earlier, rather than witness what would surely be an imbalanced mess (especially since it's SE we're talking about).