While top tier OT's in the league do make more than top tier guards, both are well paid. Personally, I loved that Samson sat and STAYED rather than transferred while he fought for reps at guard. He was a 5 star OT prospect coming out of HS at 6'6" and 330. If an OL prospect isn't willing to play another position other than OT, pass. Samson may end up at OT at some point in the future, but he was not going to see reps behind CiCi and Markel. He manned up, slid inside (pause) and gained valuable playing time.
I wrote all of that as a back drop for Congdon and the guard commentary. In time, I think Congdon will be a stud. Great size (pause), family, seems to have his head screwed on correctly, etc. However, last I heard, he was up to 330 after being listed at 285 on his recruiting profile. It will take him some time to learn how to play with that new size (pause) AND how to play at this level. I hope he redshirts and follows the Samson plan, not necessarily shifting inside to Guard, but being flexible enough to play multiple positions. OGs are getting more and more athletic and seem to be tracking more into the old leaner OT frames we used to see and less in the Navaughn Donaldson slop mold.
Now that you've suffered through two paragraphs of nonsense, the answer is simple - you take Mark Mathews no matter what. Dude is somewhere between Cantwell and CiCi and Lord knows, you never pass up dudes like that. If one of Cantwell, Congdon, Ervin, or Mathews ends up at guard, so be it.