It isn't totally fair to compare it to the last election in 2012. We actually had an election in 2010 and Wilders got 24 seats, 4 more than he gets now. After that he was in a coalition with VVD and CDA, but the coalition collapsed rather quickly. Mainly because of fighting within the PVV party and general uncooperativeness by Wilders. The voters punished him the next election + it was a horse race between left (PVDA) and right (VVD), meaning a lot of people voted strategically. Therefore, Wilders had only 15 seats in 2012.

With the added fact that since 2010 we have had: (islamic) terrorist attacks in Belgium, France and Germany + Syrian refugee crisis + ISIS + Turkish upheavel, the PVV should have fared well in this climate. The fact that Wilders did not return, or exceed his 2010 level of seats is thus considered a (small) victory against populism.

I agree with you that the results show that (anti)-immigration is still an important facet in people's voting behaviour and that is partially why VVD did so well, but I do strongly believe that VVD is not anywhere close to PVV.