Eh, I don't know if Karl specializes in marksmanship at all. I think Ian's relationship with Karl is closer to that of a personal friend who he can do stuff like go to and organize matches with. Karl routinely gets better times than Ian, but I don't think I've ever seen a controlled demonstration where Karl is a better shot on paper. It's more like he's more practiced going through stages/shooting practically while Ian spends a lot of his time talking about history and research, and using that they are able to intersect their experience into cool thought experiments people may have thought of but not really engaged in due to the current gun community's focus on self-defense/tactical application.
Things like building a concept AR based on Stoner's original design principles, running action matches with outdated or weird guns and applying modern doctrine to them, comparing two different approaches to a similar role, mudtesting guns to see what is and is not truly reliable since soldiers might not have the best perspective or intentions when it comes to talking about guns they've used or faced off against, et cetera et cetera. That is the niche InRangeTV truly fills.
When was the last time you saw any major gun channel do anything other than shoot a few hundred to a few thousand rounds through a contemporary design and say it's good? Way I see it, Ian threw the FR F1 over to 9 Hole because they are better capable at filling the niche of Infantry and Sniper marksmanship, with a retired Army officer who's been to a lot of places and messed with multiple different weapon systems and a competitive shooter with actual wins under his belt.
I don't know, not trying to put words in your mouth but I sincerely don't see any rift between Ian and Karl. It mostly boils down to shitposting over Karl's weirder lifestyle.