I'm just imagining a skybreaker going full division flying through some skyscrapers in Scadrial 9/11 right now, thank you sir.
So, I'd say the only ghostbloods allowed are scasrian natives. And Kandra cannot mimic Radiants, or singers, and any Elsecaller, Lightweaver, or Willshaper can see what they are by looking into the CR.
Actually it would be fine.
Additionally they can use Tai-na gemhearts to store stormlight, or use cohesion to make larger perfect gemstones.
Let's assume this works(which I believe it will) that's one person, and only so many attributes. Have Elsecallers soulcast an aluminum box around him, harry them with Windrunners, atrack with Lightweavers, jusr wear them down. They'll run out of attributes eventually.
The lerasium only appeared once, and hasn't been able to be replicated. And Wayne ate all of it.
Inqusitors have to rest a lot and it gets worse as they get older. I doubt Marsh can manage more than a few active hours a week. Additionally he isn't fullborn, he only has 21 spikes, 2 are for Atium, and there are probably multiple a-steel ones.
Scadrian airships make about 25 mph, and can be brought down by a single squire.
A rosharan will be heavier than their scadrian counterpart.
Sibling sheild generators should do the trick.