You have to keep in mind that VW so far was the team with nearly unlimited budget. Remember what happened in GB? All cars had transmission issuses and they solved it overnight. So, and if you look how many parts they are homologating over year, then with semi private team, there is always risk that official teams can do more or teams with more cars can do more. Imagine M-Sport having 5 cars like Wilson is dreaming? And VW only two, that means 2.5 times more testing during real competition. So, in short term, Polo is probably fastest.. but long term? Do they still have all the technical staff or some have already left to other teams? this is unknown factor and risk.