The more I think about it, the more I'm convincing myself that fixing the forward depth is a higher priority than defense.
We have 4 legit top line forwards (Hischier, Bratt, Hughes, Meier), 3 middle sixers (Haula, Palat, Mercer), one solid 4th liner in Lazar and one mediocre 4th liner in Bastian. Holtz started the season well but has really only played a handful of impressive games since November. Maybe you can add him to the middle six group if he can be more consistent.
Halonen, Bowers, Willman, Dowling all played minutes for us this year. MacDermid has "played" 15 games. Tierney has played 51 games. Tierney is going to come in 13th in ES TOI this year and 2 of the guys above him aren't coming back. He was meant to be AHL depth. I had high hopes for Foote coming into the year and it seems like the org did too. It's probably too tough to go from AHLer to effective regular after not playing for a year.
Palat-Hischier-Bratt
x-Hughes-Meier
x-Haula-Mercer
Lazar-x-Bastian
Foote, x
I'm presuming Holtz is getting traded, but that's at least 3 forwards they need to hit on even if not. Not to mention it would be preferable if they could add 2 top 6 forward that would push Palat down. If you can keep Palat and Haula in the bottom 6 more often than not and keep Lazar on the 4th line and add a true anchor 4th liner like McLeod was it will go a long way toward building a team that can hold onto the puck in the OZ/NZ more often and mask the defensive deficiencies. If one of Bratt/Meier/Mercer/Holtz could be an effective LW that would help a lot with the balance.
That all hinges on Hamilton coming back near 100% and his presence improving the play of Marino, Bahl, and Seigenthaler. I'd personally still want to upgrade the top 4 LHD, but I think getting those forward additions right (and coaching/goal) is going to be more critical.