Let me preface this to be safe: I don't think Staal is good.
Having said that, I DO think that Staal is an excellent partner for Tony - in principle. His game is essentially built to support Tony and nothing else, by maximizing the time he can play to his strengths, and minimize the time spent around his weaknesses.
- Staal's job is to be first one into the corner on a dump - potentially Tony's biggest weaknesses. It's not a strength anymore since he only has one eye, but in a past life it was, and you can tell he's at least comfortable doing it and allows Tony to not have to.
- Tony's biggest strength is when the pucks on his stick - when Staal gets it, he's moving it d to d. On the blueline in the O-zone, regroup in the neutral zone, or breakout in the d-zone - his first look is always to Tony.
Again, I don't think Staal is good. And if you could replace him with someone else who does these exact same things, but also isn't bad, that would obviously be a huge plus over the present situation. However, I do feel there's a solid point to be made that Staal actually does provide some positive value to Tony, by being partner that basically exists only to cater to his strengths and mask his weaknesses.