We have Edvinsson coming up, who looks similarly gifted as Seider, but we'll see...
Maatta and Walman have at least enough offense to not be zeros there...
So yes, play tough defense, add toughness to the team in general, win puck battles and be able to move the puck or pass it to get it out of our own zone. That's what is the primary need for the rest of our defenseman. Any additional offense, on top of those factors... is icing on the cake.
Primarily... I think Hronek did not meet any of those factors and was moved as a result.