Not sure how GC are getting screwed in this deal? They're getting JDG plus pick 9 for Lynch (and keep their existing pick 3). And for the purposes the official trade, we're swapping JDG for a 5 place pick upgrade to a top 5 pick and getting Lynch as FA.
In terms of collusion, I think JDG is clearly one of those players where his value is so varied in peoples eyes, it'll be hard to prove that it's a trade specifically to benefit GC and offer them something more on top of their FA comp. On one hand you can argue the JDG is a former pick 5 about to breakout in the perfect age bracket worth a top 5 pick on his own like the Weller for pick 2 trade GC did last year. On another hand you can argue that he's a talented kid who has massive off field troubles and baggage and is only worth a small pick upgrade like the Cam McCarthy trade to Freo.
A) Please stop ignoring the compensation pick 4 they're giving away as if it's not something they would otherwise have if Lynch left as an FA.
B) Any time we offer GC something to get them to not match our FA bid it is 100% collusion.
C) GC would be getting swindled I can't really make it any clearer than the previous reply - ie. they would be losing the best player and high pick in exchange for a lesser player (who may or may not be at the elite level at some point in the future) and a lower pick. They would also be losing out on grabbing one of the top 4 kids, which at this stage look like Lukiosis, one of the King twins or the "best" midfield prospect.
I don't know how you can not think they aren't getting absolutely swindled there - keeping their pick 3 has no relevance whatsoever.
p.s. GC stupidly overpaid for Weller - they sold the farm worse than we did in grabbing Murray (mostly because they dicked around and left the trade until the very last minute just as we did).