The Steelers have cap room, so I don't care if they pay him or not. It can set a precedent, but then again, they can tell anyone they want yes or no. Cam is just coming off as real whiney a year after agreeing to a contract he didn't have to.
But to your point about him being a top 15 DT in the NFL right now, is Patrick Mahomes a top 5 QB right now? He's tied for 14th in average pay for year, with Kirk Cousins, a backup QB. He isn't a free agent until 2032. It was a great contract for long-term security, but terrible for overall value. I don't see him complaining about not getting paid enough.
The problem with the NFL right now is the "next guy" is always becoming the highest paid, whether or not they are the best. Factor in that older players will never be paid at the top of their positions, Cam is where he is right now.