If Lesnar getting the shot at Randy proves anything its not who deserves what but what the fans will pay to see and Carwin/Lesnar is money, it is the epic battle of the giants and Id almost guarantee we see it before years end.
Lesnar got the shot because of his name. Carwin doesn't have that luxary. Lesnar/Carwin would sell for sure, especially if its for the title. But I don't see them just going oh hey guess what casual fans we have a guy just like Lesnar and their gonna fight for the title. Carwin needs at least one win over a big name on the main card before getting a title shot.
Now if Lesnar doesn't win the tourny then maybe we would see Carwin/Lesnar as Carwins first big name fight but even then I wouldn't be so sure.