If people think that RB has poor positional value, I just don't get it with TE.
Incoming: Kelce!
OK, let's talk about that. IMO, no position benefits more from a QB than TE. Some people talk like Kyle Pitts is a disappointment. IMO, if Kelce was on Atlanta and Pitts in KC, people would be talking about Pitts as the GOAT. Don't get me wrong, Kelce is certainly a very good player but the fact that he plays with a QB who frequently escapes pressure and finds him really pumps up his impact.
When you watch the "highlights" of guys like Mayer, they really aren't creating offense as much as they are being the recipients of it. There are a fair number of people out there that can do some blocking and go out 5 yards and turn right. That's oversimplified but TE's rarely live at the edge of human athleticism like WR's. Like RB's, these type of players are frequently available and with rare exception, the marginal utility of one over the other isn't significant.
IMO, Dallas still has needs at RB, LB, G and maybe WR. All of them can provide more positional value than upgrading from Ferguson to La Porta.