Are shards different?

[MikkoAkure]

I also suspect that due to each shared having significantly less aether, they will be rather weak compared to those on hydaelen. Like how nobody on the first had ever summoned voidsent because they simply packed the aetheric density without literal generations of controlled breeding and planned marriages to cultivate mages strong enough to barely open the way

The characters on the First you're referencing were attempting to open stable Voidgates, which is an entirely different realm of aether required compared to Voidsent summoning. Considering the fact that the people there knew about Voidsent enough to create a breeding program in order to make children who can open stable Voidgates, it's otherwise not a problem, except for perhaps the distance between the two Shards.

There's also the fact that the Allagans of the 3rd Astral Era and the Mhachi of the 5th were less joined than we are and did not have the benefit of a recent Calamity, which also weakens the barrier between the Void and the Source and they summoned WAY more Voidsent than anyone in our modern day has.

Garleans also have no ability to manipulate aether at all but still somehow are able to contact the Thirteenth. I don't know if that was an oversight though.