Well, the Clalit preprint relying on more data by an order of magnitude will be out soon, and that should be the definitive analysis.
However, current results for a Pfizer 1st-only regiment aren't very encouraging IMHO. It's possible the first dose starts to be really effective exactly at the time Pfizer suggested to have the second dose, and that this increase is rather sharp - But it would be some coincidence, and antibody tests (showing not so good efficiency against variants following 1st dose, and also much larger antibody count after 2nd dose) are contraindicative.