I actually understand what Motown is arguing but he is off a bit
Even if you have said rookie on a contract, in year 3 he isn't signing for full free agent value. He wouldn't have played or shown what you can do so nobody is giving him 40 million. And not many guys are extended then. If he was the cap hit would be backloaded like all contracts.
So there still would be savings by drafting one and letting goff go.
Goff best case one
Year 1 of just Goff with a likely restructure
13 million
Year 1 of goff and rookie
Goff 30 million + rookie 5 million
Next savings of -23 million
Year 2 of just goff
28 million
Year 2 of goff cap hit because hes cut and rookie
15 million
Net savings of 13 million
Year 3 of rookie
15 million
(Net savings of 25 million cause goffs extension would be about 40 million for arguments sake by then)
So while it wouldn't help the cap this year, per se. It would in the long term. And the idea behind this year's saving assumes one thing and forgets another. Someone is getting that rookie cap hit no matter what. And it assumes goff would even agree to a restructure.