Gudbranson plays the role Tanev plays, except Tanev is much better at it.
The last few years in the playoffs, the Leafs played well defensively and were very hard to score against. They didn't go far because their offensive stars were shut down.
They badly need a top-end puck moving offensive defenseman to complement their scoring forwards, and to create 3 on 2s and 2 in 1s, and more high danger scoring chances, which they never seem to get enough of in the playoffs. I said top-end, not a 4-6 guy like Ekman-Larsson. They can be 2-way like Montour / Forsling, or Theodore / Pietrangelo, Hedman. Or offensive like Bouchard or Makar.
This holds them back more than anything. They don't need another defensive guy that can't move the puck. They already are very tight defensively in the playoffs.