First of all, Scheifele signed a 6.15 or so contract and not 9-10mil/ 8 yrs contract. It is a lot harder to exceed 9-10mil a yr than 6.15mil/yr.
It is still a long term 2nd contract, which at the time still had some risk associated with it. His first 2 seasons did not scream future superstar.
Secondly, what do you think Scheifele next contract will be? Probably around where JT is if not more. So what does giving players an 8 yr deal with huge money right off their ELC help with the team Cap? By bridging them like 4-6 yrs, the team get to lower their overall caphit and get to sign and resign better players to build a stronger team. Then when time to renew the core to big contract, you pay the core accordingly for 8 yrs. It helps the teams cap by having their superstar on a sweetheart deal for 8 years. One that's a pretty big window. Two that gives them team plenty of time to prepare for his 3rd contract. Pretty sure any team would love to be in that situation.
Take McDavid for example.
18-20, he is on his ELC
21-28, 12.5mil/yr
29-36, most likely be 18mil/yr, since it is 8 years from now. Nomatter what, he is not going to take anything less than 12.5mil unless he is injury prone and assuming the cap keeps going up every year.
Let's not argue is McDavid worth the contract, but says Oilers bridge McDavid by offering 10mil for 5 yrs. Thus, the AAV on his second contract is 2.5mil less. Then Oilers get to resign him 3 yrs earlier than above scenario, which is safe to assume if will cost less than resigning him three years later. Not sure why you keep mentioning 5 years as the bridge contracts, teams would be pretty foolish to allow their 25/26 yo superstars to hit ufa. In your example McDavid walks away from Edmonton in 5 years.
To me, it is a no brainier to try not to give players an 8 yrs deal right off their ELC.