In what sense are we speaking? At the draft, in trades, in general?
From the draft, fans are highest on the forwards as defensemen take longer to develop. A top 3 pick would mean we take the best pick available which ends up being a forward. Below that, and it depends where we land and who has been taken ahead of us. There are 3 LHD we could reliably choose from, but it's uncertain how long they would spend developing for us.
From trades/free agency? Probably looking for a forward in the top 6 to replace Ladd at least short term, especially if we don't get a Matthews/Finn who might be NHL ready now. Kyle Connor hasn't secured a spot on the team yet, let alone proven he can handle top 6 minutes against top competition. He'll get the Ehlers treatment on the 3rd line until he's ready if he plays with the club.
So basically, I'd say it's because we have so much youth that we don't have enough high end developed talent ready to play big minutes. Ignoring the draft, we have Wheeler/Scheifele/Ehlers/Little up front in our top 6. Supported by a ton of middle six/bottom six types (currently) like Perreault/Stafford/Petan/Dano/Armia/Burmi/Lowry/Copp and more. Connor projects to fit into the top 6, but I doubt it happens right away, even if it does they're still stuck using Perreault or Stafford in the top 6 to compliment the second line. Perreault's fine, but any injury to the top 6 and a guy like Stafford who's seemingly on the downswing moves up which doesn't help us much. I liken it to the usage of Thorburn above a 4th line role, he just shouldn't be playing there on our team.
Short term, defensively.. Trouba moves to the left side and then Stu gets moved to 7th D. Morrissey or Chiarot on the left side with Trouba+Enstrom completed by Buff/Myers/Postma on the right side. Most of that top core isn't going anywhere anytime soon. Enstrom can be replaced in a few years by our 1st pick this summer if there's no high quality forward left to choose from.