It's exciting to see the production from Mailloux in the AHL, but as it's been mentioned earlier in this thread, it's all about him hitting a baseline of defensive reliability so he can take regular minutes in the NHL.
Evan Bouchard couldn't stick with the Oilers until he was 22, and he still had some pretty glaring defensive issues (and still does today). He was chosen much higher than Mailloux.
There's no guarantee he'll hone his defensive game enough to take Top 4 minutes, but Mailloux is just 21 so there's lots of runway still for him to develop and grow.