This isn't accurate.
After Strange re-injured his knee week fifteen in Kansas City, Mafi replaced him and started the next two games. Jake Andrews started the last game of the season. Why we don't know for sure, maybe injury, poor pay by Mafi, maybe he hit a wall, maybe they were playing for the future and getting Jake valuable reps that he didn't play early in the year. Mafi played a lot more, started more, and for stretches all season long.
Mafi is only a guard as far as we know, Robinson played guard at Texas A&M... Jake Andrews played center.
Onwenu is probably staying at right tackle, the Patriots said earlier this year they viewed Sow and Strange as the incumbent guards... which means they were happy to have Onwenu at tackle and paid him as such. If Mafi and Robinson suck, I could see them bringing Onwenu back inside and using their lesser tackles outside to protect the interior of the pocket... but I doubt it.
Simply because between Calvin Anderson, Caedan Wallace, Chukwuma Okorafor, Zuri Henry and Tyrone Wheatley they should be able to find a left tackle. Between Antonio Mafi, Calvin Anderson and Layden Robinson they should be able to find a starting guard. Between Jake Andrews and Charles Turner they should be able to find a backup center.
Based on Sow on the left side instead of right it will probably look like this:
LT – Chukwuma Okorafor, Caedan Wallace, Calvin Anderson, Zuri Henry (PS),
LG – Sidy Sow, Cole Strange (PUP),
C – David Andrews, Jake Andrews, Charles Turner (PS),
RG– Antonio Mafi, Layden Robinson,
RT – Michael Onwenu, Tyrone Wheatley (PS),
Mafi is not a sure thing, he once weighed 411 pounds in college. He slimmed down to 340, so we know he can work on himself, but he had to keep working hard on himself this offseason. The year two jump is the most important one.
But NFL experience and playing time counts for something, it's a tall ask to assume middle round draft picks who didn't lift at either the combine or pro day are going to be strong enough to start this season.