All three were spectacularly good, and also hugely unlucky. In my opinion, Cevert would have won at least two WDC, and Alesi should have won at least one as well. Its hard to tell what Kubica would have done, but I think that given the car, he would be challenging for championships as well. So sad to see all these drivers title less :(
It’s always difficult to compare drivers who competed full career and those who had a career cut short.
Of those single GP winners, I think the following had an early end to their careers: Kubica, Nannini, Nilsson, Pace, Cevert, Scarfiotti, Bandini, Musso.