So, I think this illustrates the problems with the NIL system being separated from the school. You can't claim poaching or recruiting tampering if the staff in question didn't offer him anything.
I'm not sure what the story is, but with Mickey leaving ND in the same fashion, I think you're going to see this 4 game window to redshirt used from time to time moving forward as part of the system working as intended.
The hard truth is that Sluka doesn't have any chance of making it in the NFL as a QB. His window to make 6 figures a season is extremely limited and if someone offers him more than what you can counter and he can leave, he's going to leave. This is how capitalism works in a system without any oversight or guard rails. I hate that he did it as a rebel fan, but as a capitalist it seems like if you didn't want the system to work like this you would have put in rules against it.