Actually.... When Crosby signed his deal, the first one out of his entry level contract, the % cap hit was 17.3%.
https://www.capfriendly.com/players/sidney-crosby
Shows it right there.
Cap this season is expected to be $75M. Mcdavid at $13.25 us 17.6% of that. Pretty much spot on.
Not to mention this Mcdavid contract kicks in followin NEXT season... so in 2018-19....When the cap is likely even slightly higher.