No offense, but Matthews hasn't proven anything yet, so I don't know why he is "very rare." The guy hasn't even cracked 70 points in a season yet regardless of his injuries last season. Until he actually takes that next step, puts up 90+ points in a season and actually shows up in the playoffs, you can't consider him a generational talent, like most Leafs fan seem to think he already is.
As I said, the trade itself, hurts the Flyers. Hextall's two main pieces for his re-build are Provorov and Patrick. If the Flyers make that trade, yes they get Matthews, but then who is their #1 defenseman?