I agree with you in principle, but I think all they're really saying is that it affects the conversation, which is literally what a contract negotiation is. So of course it matters. It clearly helps establish the local market and is a key reference for each side setting their price.
Sure, but like you pointed out, that's just one argument in the conversation. The logical counter is "Sure, Panarin got that percentage, 5 years ago when we weren't the odds-on favorite to win stuff. Now that we ARE that team, we'd like to REMAIN that caliber of team because we all want a fist full of Cup rings. We can't do that if we get too top-heavy on contracts.
"Panarin got that money at that time because it takes that kind of investment to prove to the team and the league that we want to build a winner. Your client contributes mightily to our success and we're grateful, but here's a mountain of historical stats versus contract dollars and term that proves pretty conclusively that goalies don't have the shelf life that wings do. We can't build that winner pretending that your client will defy that trend."
I think CCR is right that ultimately the cap percentage of other, wildly different positions isn't likely to land Shesterkin that kind of money. It's absolutely a factor in the negotiation that may raise what he gets a bit, but he shouldn't get that kind of money for max term unless the Rags are dumb.