I see your point. WRT DeMelo it's more of a development thing. He's been solid the past few weeks, and I feel like benching him for a guy like Russell who wouldn't add much (imo) would be a roadblock for him and a waste of assets and cap space for us.
I don't think it's a development thing for DeMelo. He's not going to get much better than what he is right now. He's a fringe NHL'er. Russell is significantly better than that and offers a set of skills that this Sharks team could definitely use especially at that level. A 3rd pairing d-man that can move the puck well, QB the 2nd unit, and be put in a spot on the PK to move Burns off the PK is a pretty decent add especially if utilized properly. And honestly, I don't see very many better options and I don't think he'd cost that much.