I am not sure anyone suggests it being any lock at all. He still needs to earn that position.
The issue you are running into is arguing that Wynn was drafted with the interior in mind because he lacks the size to be a NFL tackle.
Even the outcome is the same that is a totally different take than suggesting that he might end up being a guard if it doesn't work out.
At least one poster did, and wasn't it you who said Wynn was drafted because he was the best tackle in his draft class, omitting the two guys taken ahead of him including the one taken at #9 overall. I already said this:
"Do I think Wynn could play tackle in a pinch, absolutely, so could any of the offensive linemen on the field or bench, who is best for the job is what matters." - Me above
Mike McGlinchey and Kolton Miller were drafted ahead of Wynn, Pats had Miller in for a pre-draft meeting and likely would have grabbed him if not for Oakland. Everyone had Wynn pegged as a guard, not just me. He is and was one of the best offensive line prospects in his class, his better more natural fit is guard.
Cajuste may be healthy enough to compete at tackle, Croston has always been talented but had to get stronger, Thuney also played some tackle in college, Froholdt among all the rookies is probably most ready to step in and play at guard...
Wynn is coming off an achilles injury, there may be better options at tackle, he might be better served getting eased in and taking over at guard next year when Thuney walks. Veldheer retiring creates a little more uncertainty, health provided he was the starter.
Trent Brown got the opening day nod at left tackle last year in camp, it was never a given Wynn was going to start at tackle, then or now.