Would a 80-90p center be worth a 85-95p winger + 65-75p center ?
The 93-100 point centre, you mean, based on a full season? If you are going to call Monohan a "65-75 point centre" based on him hitting 65 once in his seven years, then you have to say Matthews is a career PPG who is probably going to hit 100+ points consistently moving forward, seeing how he is pretty much there now, at 22.
For shits and giggles, let's look at MacKinnon and Matthews in their first four years in the league:
MacKinnon 300 GP, 75 G, 206 points
Matthews 282 GP, 158 G, 295 points
In 18 less games, Matthews has 83 more goals and 89 more points, which probably explains why he is virtually untouchable. No offense, but it's not what Matthews could fetch in a trade, it's what the Leafs are losing. It's not hyperbole to suggest, if he spends his entire career in Toronto, he COULD go down as the best Leaf ever. If not the best, definitely one of the best.
Matthews is 22, and is only going to get better. That said, it's not the quality of the players coming back, it's the fit. We don't really save any money, and both are UFA in the next two/three years and will get raises and Leafs don't need top-6 help. Unless Monohan or Gaudreau answers the defensive problem, it isn't a fit for the Leafs.