My lore knowledge in GKs aren't that good, since they're often the "taboo" PCs and no GMs allowed me to play them in the past. Though what you've said does make sense I supposed. *shrug*
As a funny side note, IIRC, they are even discouraged in Dark Heresy even though there's rules for them! I actually don't hate GKs, but the reason I wouldn't allow them in 'mixed' RPGs is because their skillset is either inadequate (Xenos) or outshines all other non GK characters (Daemons, Chaos Space Marines depending on how you put it). Good on Urian for doing so, though. I like LK's role in this squad and am curious how the squad will develop.
they are also pretty good at fighting chaos worshipping Xenos pretty much anything warp afiliated should fear GK
Oh, I know. They are always psyker SMs, even when not battling heretics. I just mean they'd have a looooot of skills and knowledge of Daemons that wouldn't see use in a xenos based campaign. Like taking a techmarine on an expedition through a Tyranid ship or a Magos Biologis against Necrons. Still good at what they do, but their specialist skills are not as useful.
Kan ey has Banisher... Or demonhost? A certain astropath might make a good host. Just an idea. Would love to RP with Uriel again!
not necessarily born with, can be in the gene-seed, see Thousand Sons. But in case of GK it's a born trait - yes. You can make stuff up and attempt whatever you want - if it succeeds, whole different story. And if mr. half dead (aka critical condition) tries to be the 'core-sorcerer' then except shit to happen since he is physically pretty.... well you know! Banisher yes. No daemonhosts, no astropaths. Virgil would be unfit to be trained to a Banisher.