Yup, we should pay $10M for a player who has almost no experience at LG. IF we could draft a starting rookie LT at 21 (not likely), then We should trade Wynn for whatever we can get a sign a starting LG later in the draft or in free agency. We are very likely to be able to find a better OG than Wynn in the 2nd, 3rd ior 4th, or even in free agency for the $10M we would save from trading Wynn.
TO BE CLEAR
I am 100% fine with drafting a LT in the first if we think that he is a better starter in his rookie year than Wynn is now. My suspicion is that even this player that you think is a starter is indeed available, he might be drafted and spend a year as a swing OT, with Wynn still starting at LT.
ONE BOTTOM LINE
If Wynn isn't starting at LG, he isn't worth $10M as a starting LG. He may or may not be worth $10M as a backup OT. More likely, it is better to trade him for a 6th and use the money for someone else, IF HE ISN'T STARTING AT LT.