You'd think so, but Dermott hasn't been promoted in three years, and Sandin was paired with Barrie and Liljegren during his callup.
For a team that integrates forwards so well, the Leafs defensive development has been absolute shit.
Q-F-T -- Seriously.
They've got 4 reasonably young defencemen who need to play (Lehtonen, Dermott, Liljegren and Sandin), but realistically, only room for 1 because they all play the same style.
I think the problem is -- since Dubas took over, they have seemingly built from the middle-pair of the defence, outwards, rather than prioritizing the top of their D, and then figuring out ways with which to integrate the youth they have.
You have a quite competent top pair of Morgan Rielly & Ron Hainsey. A mediocre 2nd pair of Gardiner & Zaitsev, and a decent bottom pair with Dermott's upside & Ozhiganov -- knowing that Liljegren is coming soon. You know Gardiner is leaving, and probably suspect that Zaitsev wants out.
He could have said to himself-- let's get a high quality, defensive minded, right shot who can maybe play with Rielly on the top pair, maybe play with Dermott on the 2nd pair, regardless give us flexibility to move Hainsey down the lineup as he gets older -- and accept that maybe Ron Hainsey is the ideal partner for a Timothy Liljegren to come into the lineup next year.
No, instead he goes out and gets Jake Muzzin, only to find out that he & Rielly both really need to be on the left side; so now he's stuck rebuilding his 2nd pair; and goes off and trades for 1 year of Tyson Barrie to give the team even more offence from the backend -- because he & Muzzin should have made for a good 2nd pair.
At this point, the Leafs have built their top 4 with Rielly, Brodie, Muzzin & Holl, and it's really not a bad one especially when you consider that I think Brodie & Holl may be interchangable.
Beyond that, they've gotta take the 4 potential guys they have -- and key-in on one or two of them as "we're going to develop this player". One will be the #5/6 defenceman, the other can be #7, and let Rosen/Marincin battle it out for #8.
The others need to be jettisoned before their value drops to zero, and they need to bring in an experienced body to help foster that development -- somebody who compliments whomever you've picked. At this point, I do believe that you have to move on from Dermott, he needs more opportunity than playing behind Muzzin & Rielly are going to give him. Sandin is a more logical fit on the 3rd pair.