When you look at Nylander's numbers from last season, he was above a point per game and he also scored 40 goals. Those types of players don't exactly grow on trees. Nylander has all the skill in the world, but there are parts of his game that are lacking, like the level of physicality and a commitment to backchecking and playing on the defensive side of the puck.
Paying William Nylander $10M isn't going to magically turn this core into a winning core. The same can be said about hefty pay increases for Matthews and Marner, but at least they have the luxury of being considered elite players at their position.
The fact of the matter is that if you're looking at the big picture, paying Nylander more money won't equate to any more playoff success. Instead, it will be taking money away from being able to shore up other areas of the roster. Yes, the cap is expected to go up. Yes, John Tavares is on a contract that will expire 2 summers from now. But if the goal is to compete for a Stanley Cup every year, I'm not sure shelling out a larger salary to Nylander, who doesn't commit to a 200-foot game and who isn't exactly a physical presence out there in the playoffs, will help the Leafs take the next step in their pursuit of glory. Just my two cents.