Pis didn`t win because it was so strong , they won because a few smaller parties didn`t reach the minimum
Yes, and because the centrist vote split between PO and Nowoczesna, PiS managed to win a few additional seats that they wouldn't have won otherwise. The electoral mathematics are quite complicated, but in terms of pure votes, PiS scored marginally (less than 100,000) more votes than PO did in 2011, and only won about 700,000 more votes than PO/N. combined.
It's quite interesting running electoral simulations with opinion poll results. For instance, let's take the averages from the polls on ewybory.eu. I come up with:
PiS (38.50%): 193
KE (37.39%): 188
Wiosna (10.00%): 50
K'15 (5.76%): 29
Konfederacja (4.89%): Not enough votes
Razem (2.83%): Not enough votes
KE+Wiosna would have 238 and a majority.
But what happens if Konfederacja make it along with K'15?
PiS (38.40%): 184
KE (37.30%): 178
Wiosna (9.97%): 47
K'15 (5.75%): 27
Konfederacja (5.12%): 24
Razem (2.82%): Not enough votes
PiS+K'15+Konfederacja would be on 235 and a majority.
Let's say Konfederacja finish off Kukiz and take most of their support:
PiS (38.64%): 188
KE (37.53%): 183
Wiosna (10.04%): 49
Konfederacja (8.37%): 40
Razem (2.84%): Not enough votes
K'15 (1.93%): Not enough votes
Because d'Hondt rewards bigger parties, such a scenario actually punishes Konfederacja. It would leave KE+Wiosna on 232, just enough for a majority.
This is why Pawłowicz is right when she says that every vote counts.