I firmly believe that the Mets are much better off with Bichette at third base, than they would be with a posible platoon of Vientos and Mauricio. I really don't want Vientos/Mauricio playing major (starting) roles for the Mets.
Vientos has had one productive season as a hitter. Even then, he struck out 1 out of every 3 at bats. The other 3 seasons, including the past two he is a .230 hitter that doesn't walk, doesn't run well, and is a defensive liability at both corner infield positions. His only real asset is that he has power, but a "swing hard and hope you occasionally connect" type of hitter is not what I want Mets to build around.
Mauricio has not had as much opportunity to prove himself at the Major League level, but he has failed to reliably produce when he has had a chance. He is so bad as a right handed hitter, I wonder why the Mets don't have him bat exclusively from the left side. He at least has the ability to play adequate defense at 3 infield positions. Hopefully, he can be healthy and productive in the future, but I find myself doubtful he will be more than a left handed hitting utility infileder/DH role player. Rather redundant with Baty also on the team.