He had one season where he played on average 21 mins a night the rest were 19 mins to 18 mins.
That really does not scream to me top pairing. If we are having to shelter Franson for him to be effective who is going to get those extra mins? Robidas and Gards?
A top pairing defender like Phaneuf, Chara, Suter, Campbell, Weber, Hamonic, Seabrook, McDonagh/Girardi or Bouwmeester are considered minute eaters because they play top PP, top PK and top pairing even strength. Outside of Suter & Campbell, most of these players average around 23-25 minutes a game. These players also average anywhere from 3-5 minutes on the PP a night. So if we assume Polak will be no where near the PP, I see no reason he cannot have been or in the future play the top pairing even strength while still averaging around 20-21 minutes.
Phaneuf - 3 MIN PP, 4 MIN PK, 17 MIN EVEN = 24 MIN
Polak - 0 MIN PP, 4 MIN PK, 17 MIN EVEN = 21 MIN
Gardiner - 3 MIN PP, 0 MIN PK, 19 MIN EVEN = 22 MIN
Robidas - 0 MIN PP, 2 MIN PK, 19 MIN EVEN = 21 MIN
Rielly - 3 MIN PP, 0 MIN PK, 12 MIN EVEN (SHELTERED) = 15 MIN
Franson - 3 MIN PP, 2 MIN PK, 12 MIN EVEN (SHELTERED) = 17 MIN
We can easily shelter Franson and Rielly. This is even an exaggeration, Phaneuf & Polak could easily take a couple less minutes even strength as teams tend to utilize their 3rd and 4th line more, and Rielly's minutes should increase as the season progresses.