I think Zucker would be a great third liner, but I don't know how you justify his price point in that role with the holes in this roster. Geno needs a winger who can bring some scoring potential, imo. I don't know that Barbashev, Bunting, Zucker, or Garland are good enough in that regard.
The entire 3rd line needs to be remade from the ground up to be used as the minute eating, cycle/shutdown line Sully wants. They need to perma-scratch Carter, they gotta dump Granlund or buy him out if all options are explored and the price to get someone to take him is too high. Then there's the issue of whether or not Rust continues to play at like a 45pt player who is also terrible away from the puck.