I keep hearing people assert this, but you can't at all say that based off of one single tweet that he was uncomfortable at RT at the end of the season, coming off a high ankle sprain having played on the left side all season - of course he was uncomfortable, not every olineman is Yanda and can make a seamless transition at a moments notice. With an offseason of prep it's a non-issue and people are acting as if that tweet is the big proof that he won't move under any circumstances. Come on man, one tweet given the circumstances of his trial at RT, literally the last game of season with all of the other problems, that tweet is effectively meaningless as it pertains to next season.
As far as Robinson goes, as solid as Lewis became as the season went on (btw many seem to forget that early in the season he was really struggling in the run blocking department, from the start he was a good pass protector but his run blocking was sketchy until the two post-bye games that he played) Robinson would be an upgrade at guard and is a far better fit for the "mauler" type we want compared to Lewis, who again is a natural pass protector. As far as the tape goes, everything points to Lewis being a natural OT - frame, good movement/footwork, technician of a blocker with sketchy strength, strong pass protector, etc. - and Robinson being a natural OG - mauler mentality, footwork issues at OT, strong run blocker, size, etc.