He has the highest potential of all of them for sure.
Agreed, he has legitimate 1sr pairing upside because he has the IQ and the physical tools to play against the leagues top players. I don't necessarily see that in Mailloux as he isn't as smooth of a 4 directional skater and does not process the game quick enough.
Fans get aroused with Mailloux's big shot, size and his straight ahead speed but imo no GM in the league would take him over Reinbacher. I am not crapping on Mailloux as I believe that he has some tantalizing upside but he will be one of those dmen that will make huge gaffes more often than some may be able to tolerate , much like Hutson he will have to offset the negative parts of his game with high end plays that outnumber the bad plays by a significant margin. Guhle, Reinbacher and Struble already have shown the ability/promise of much safer and predictable positive outcomes so they will definitely help mitigate some of the negative events that their more mercurial teammates may create.
With his other attributes and skills if Mailloux could skate like Beaulieu we would have a prime prospect. Until he displays better separation ability on the ice that will allow him to avoid forecheckers and consistently transport the puck from his defensive zone through the neutral zone, Mailloux will remain, at least to this observer, more a suspect than a prospect.
There is no problem with his separation speed but he does struggle at times while pivoting into a backskate posture and his back skating is below the level of the other defenders on this team not named Hutson.
He just needs to improve his ability to diagnose the play a little quicker as well as processing solutions quicker in order to dictate the play rather than chase it.