He doesn't have to become significantly better. Cap inflation will make him a 10M player under +100M cap, even if he slightly develops under his next contract. That second contract after 2024 or so could be made against +102M cap with the 4.3% yearly growth.
"Connor McDavids" on year 2024 will be getting 16 million per year etc...
Given the following assumptions
5x6 is a deal they could sign him for now.
8x7.5 is the deal they would sign him for with a max deal (because he and his agent don't want 8 years.
In his age 22-26 seasons, you are paying him 1.5M less than the long term deal.
At age 27, he renegotiates and let's say he gets 8/80. That contract runs to 35 and for age 27, 28, and 29, you're paying him 10M instead of 7.5M.
If you sign him max now, you have him till 29 and you're paying 1.5M more for the first five years and getting a 2.5M break in years 6-8. At 29, he's a UFA. You could go 8x80 for him then and then you've got potentially a 37 year old Dylan Larkin getting 10M per.
I just think it's crazy to bank so heavily on him continuing to develop to make the contract a deal when your cap savings are likely going to max out at around 2.5M a year when he's in his 27, 28, and 29 year old seasons.
Nevermind the fact you'd have to get Larkin to sign the 8 year deal which his agent is not remotely pursuing and contracts for other, similar, more proven and more talented players have ended up at 8/7.8