I don't think you could trade Greig 1 for 1 for a better player. I think his skillset is incredibly underrated and he needs time to develop.
Absolutely no reason to trade him. He should be a fixture in the top 9 for years to come.
You're going to get a lot to teams trying to throw scraps at him. Just turned 22 a few months ago, doesn't get significant PP time, and will likely produce in the 40pt range. Not outlandish to think in a couple years he'd be a 60-70 pt producer with PP time on many teams.