Are shards different?

[Cleretic]

I think it's a matter of capacity more than capability.

Ran'jit beat us in CAPABILITY. They could do more with significantly less, and, I would guess, probably would have lasted WAY less than we would have. The WoL could, in theory, outlast Ran'jit, but the issue is that Ran'jit, from decades and decades of training and refinement, had figured out how to do way more than we ever could in a single moment at this point in our lives. And the Exarch explicitly used up a massive amount of his power in maintaining the spells of the crystal tower itself I think.

Okay, then explain the bears. The wolverines, the fuath, the hobgoblins, the Ronkan constructs, the trilobites... I could go on but I think you get the idea.

I was using very direct comparisons, but your assertion that the reason Ran'jit could match us was because he was a master of combat requires every single thing on the First to also be a master of combat, because your logic would say that otherwise, the average level of things on the First would be significantly below the average level of all of Eorzea. And... well, it's not. Not one single part of Shadowbringers says that we are a superhero in this world of mere peons; in fact, everything says pretty much the opposite. We also have the persistently present example of Ryne; Ryne is also from the First, but spends most of Shadowbringers doing just fine alongside us. If your theory was true, she'd basically be a level 13 walking around in level 75 dungeons.

We've also got the flipside: when we go to Elpis, we fight just fine. The Studium fishing quests do confirm that even the regular wildlife there is more aetherically dense than in the present day, so by your logic it should be full of the hardest things we've ever had to fight... and it's just not. They're keeping pace with Thavnair's regular wildlife. Labyrinthos' lower levels are stronger.

The only source in the story declaring anything like 'more aether equals more better' are the Ascians; every single other piece of evidence that could be brought in says that's just not true, and given the fact we keep kicking the Ascians' asses I don't think even their evidence holds water. I think what actually happened there was that the Ascians latched on to aetheric density as an essentially arbitrary heuristic to declare themselves superior and all those sundered shards inferior. "We have to be better than these creatures, and we also have more aether, so clearly that's the reason our lives hold more value." Ancient techniques might be able to use more aether, but that doesn't seem to do them any good against us.

EDIT: Also, if this were true then voidsent would be completely nonthreatening, because they also come from a shard and so by your theory are lesser than Eorzean wildlife.