A few comparisons for Nylander looking at big winger contracts the last two years.
Gaudreau
Contract: 7 X 9.75M (11.82% of cap at time of signing)
Points (previous three seasons): 10th most points in the league, 20th in points per game (minimum 100 games played).
Team: Finished 1st, 1st, and 2nd in team scoring in the previous three seasons.
Huberdeau
Contract: 8 X 10.5M (12.73% of cap)
Points (previous three seasons): 3rd most points in the league, 7th in points per game (min 100 games played)
Team: Finished 1st, 1st, and 1st in team scoring in the previous three seasons.
Tkachuk
Contract: 7 X 9.5M (11.52% of cap)
Points (previous three seasons): 14th most points in the league, 27th in points per game (min 100 games played)
Team: Finished 2nd, 3rd, and 1st in team scoring in the previous three seasons.
Pastrnak
Contract: 8 X 11.25M (13.64% of cap)
Points (previous three seasons): 10th most points in the league, 11th in points per game (min 100 games played) - as he signed mid season, this was based on end of this past season.
Team: Finished 1st, 2nd, and 3rd in team scoring the previous three seasons.
Fiala
Contract: 7 X 7.875M (9.55% of cap)
Points (previous three seasons): 32nd most points in the league, 40th in points per game (min 100 games played)
Team: Finished 2nd, 2nd, and 1st in team scoring the previous three seasons.
Nylander
Contract: ?????
Points (previous three seasons): 23rd most points in the league, 36th in points per game (min 100 games played)
Team: Finished 2nd, 3rd, and 4th in team scoring in the previous three seasons
So overall, Nylander is somewhere between Fiala and Tkachuk, though Tkachuk also brings massive intangibles that Nylander doesn't bring. Nylander finished the lowest on his own team in scoring (suggesting he's likely getting a boost from playing with the players he's playing with), yet was the 2nd lowest out of this group offensively ahead of only Fiala during the three years leading up to players signing their contracts.
IMO his contract should be somewhere around ~10-10.5% of the cap, and really shouldn't be in the 11%+ range. The salary cap is expected to be 83.5M, which would give him a caphit of 8.35M-8.77M. I'd be willing to sign him in that range, but if he even wants 9M+, I would personally look at trading him.
Nylander is good, but on a balanced contender, he's probably your 5th or 6th best player once you factor in other forwards, defence, and goaltending. You can't be paying him 9M+.