Most of those premiership winning teams also had a damaging edge forward who played decent minutes:
Tohu Harris, Boyd coroner , wade graham, tony Williams (the one good year he had). Teams need both a damaging middle forward and an edge 2nd rower who causes problems on the edge
The most important assets for those premiership winning sides are their 1,6,7,9. Props are incidental and the fact that they happened to have elite props is no more relevant to the win than having an elite winger. As long as the creative players have a platform to work from there's no need for an elite prop.
Melbourne won with Ben Cross and Brett White in 2007
Manly won 40-0 with Brent Kite and Josh Perry in 2008
Melbourne won with Aiden Tolman and Brett White in 2009
St George won with Nevill Costigan and Michael Weyman in 2010
Manly won with Joe Galuvao and Brent Kite in 2011
Further, in 2012 Jesse Bromwich was a rookie, not the elite player he is now, and his starting partner was Bryan Norrie.