We do absolutely need a 2LC and maybe even a 1B goalie in addition to D. In a cap world, it is always about prioritization. I would prioritize our D for a few reasons.
The first being, we have holes there. Brodie is gone, Giordano is gone, Lyubushkin is gone, Edmundson is gone...or all are UFAs anyway. That leaves a few Rielly, McCabe, Benoit, Liljegren, and Timmins. Our prospects have low ceilings and aren't ready yet with Niemela, Webber and Chadwick. We need two top fours at least.
The next being we have lots of forwards and our prospects are closer to contributing. Centre is a weakness but we do have Matthews, Tavares, Domi (UFA, but we sign him), Holmberg, Dewar, Kampf, and Minten all options for next year. It's not perfect, but I think stronger than our D. We also have very strong wingers that can help carry lines too in Nylander, Bertuzzi (UFA, be we sign him), maybe Domi if not at C, Knies, McMann, Jarnkrok, and Cowan.
Our Goalie situation relies on Woll being good and healthy. I like Jones and Murray as third and fourth for depth and Hildeby as the unknown slotting in anywhere from 2nd to 5th. I am ok with a Stolarz or Broissant as our backup for a year or two.
Long way of saying, that I agree we need center help but we should prioritize elsewhere. The Oleksiak and Wright return for Marner is my ideal framework.