The difference is that SQ only allow Solitaire PPS members or higher in the F lounge if they are flying SIA. All the *G cards in the world will not get you in there.
To qualify as a Solitaire PPS you need to make a minimum spend of SGD250K over the previous five years with not less than SGD50K in each year and keep your spend at SGD50K a year to maintain membership.
So their F lounge is more exclusive. To access TPR you need an F ticket and again, no other way in there.