This is a loaded question-you’ll get a better answer somewhere else. Ask a rov, find a sefer that goes through the topic, etc.
@aviradearah Some poskim (including magen avraham) say if the filling is a meal type food (meat, cheese, etc) then it won’t qualify for PH’B. The Taz says like you said.
@Yaakovdoe It’s not “being machmir” to wash if the correct bracha is mezonos. The only way to cover all bases is to wash on bread and then eat the correct amount of bread to avoid shailos, but people generally aren’t interested in eating an extra slice or 2 of plain bread (especially on top of the pizza calories). So assuming one is eating just the pizza, the idea of “I’ll wash just to be safe” is wrong.
@Marxist It still depends on how much you eat and how fast.
Also, @UJM brings up a great point about the size of 2 slices.