The NFL's salary cap acts like a budget. A team can build overall roster strength by trying to make every player transaction result in a performance bargain.
There's no doubt that Taylor Heinecke offers a performance bargain for the money he is paid. There's also not much doubt that Carson Wentz is overpaid. So, when comparing the two, the significant question is: Will Wentz be so much better than Heinecke that he will more than offset the $26 million less that the team has to spend on other players in the QB's support system?
I hope I'm wrong, but I doubt it.