Why would Guhle hold himself back? Mailloux's problems are positioning and decision-making in the D-zone. If the puck is moving forward, then that's not a problem anymore. Guhle also has the skating ability to get back in time if the puck is turned over.
Hutson isn't going to be sheltered if he becomes a dominant offensive force in the NHL. Guys like Karlsson and Hughes are bad defensively but still play big minutes. Despite their defensive issues, their net impact on the ice is very positive because of how good they are offensively. You want them on the ice as much as possible.
Guhle-Reinbacher would be an awesome pairing, but you would only be able to have them on the ice for about 25 min out of 60.
If Guhle and Reinbacher are on separate pairings, then you have a really good all-around dman on the ice for 45-50 min out of 60.
A lot of teams have multiple great scoring lines. If you put Guhle - Reinbacher as a pairing you might be able to shut down McDavid's line, but then don't have much against Draisaitl's line. You can shut down Crosby's line, but not Malkin's line, etc.
Having Guhle and Reinbacher on different pairings gives you a chance to shut down the top 2 offensive lines.
Both Mailloux and Hutson have the potential to be big-time contributors when they are on the ice. By having a strong D partner like Guhle or Reinbacher, you help them maximize their potential.