There was a time when playing as a gladiator was not an entirely unreasonable thing to do. Back in ARR I would actually go gladiator to dungeons with pre-made groups from my FC because at the time it meant I had access to death blossom from rouge where I would otherwise have no AoE dps abilities (gladiator only had access to flash, a non-damaging AoE enmity skill). The only things you lost access to back then was sword oath, shield oath, cover, spirits within and hallowed ground. Hallowed and shield oath were kind of a big loss but with proper cooldown usage (gladiator had access to a lot more fluff cooldowns back then) you could make up for it while the occasional flash was more than enough to make up for the lack of shield oath. For bosses you only had your rage of halone combo back then so enmity wasn’t an issue and you gained access to a lot more burst damage from cross class cooldowns to make up for the loss of sword oath and spirits within. Basically back then you were giving up a bit of defence to boost your offence.
I was an early adopter of the idea that tanks could dish out decent damage if you let them, I’d tank in sword oath, I used STR accs and there were times I’d get flak for that but there were also times where people would praise the fact I was out dpsing some of the dps. These were the kind of things that actually made things more challenging but came with a benefit of faster dps if you could do it right and eventually became the meta.
But those days have long since gone. Classes have been left so far in the dust there is absolutely no reason to be one past level 30. Not only do you not gain anything for it since the cross class system is a thing of the past so you’re just giving up having access to a bunch of abilities past level 30, but even your stats are gimped, so before you even take abilities into consideration you’re already weaker than a PLD.
There is no pride in playing the game as a class. You are just gimping yourself for no reason. It’s no different to saying you beat the game using only fast blade or while playing without a shield equipped. There’s no benefit, you’re just handicapping yourself and your group.