I have to think the Steelers offer him enough to overcome any thoughts he might have of say a one year deal with the Rams to play for McVay. I think Mayfield would want to play for McVay. Just a hunch as I recall a story a while back before the draft of McVay happening to be on the same flight as him. If those two talked ball I am sure he remembers that and given McVay's success it makes sense that he'd want to play here briefly like this year and back up Stafford in order to spend that year and get his BS together.
But no player would overlook a strong offer from a team like the Steelers. I wouldn't.