If the Leafs wanted to pay Nylander a fair rate just based on what he'd already proven my hunch is he'd be signed to a short term bridge deal at 6 million or so per and back in the line-up.
The issue here is that the Leafs almost certainly want Nylander to sign a short term deal that artificially depresses his salary because of his RFA status or they want to sign him to a long term deal at his current market value that allows for no renegotiation as he, hopefully, gets better and is worth more. If what they're reported to be offering is true, it leaves virtually no room for Nylander's growth relative to his salary.