To me an"icon" is someone that is very good at their chosen sport and has a profile outside of it that the media can pick up on that probably clouds the issue a little
Reporting on car racing drivers 50 years ago was a bit different to today and would hardly make a daily paper unless they had won the F1 title of the year or they had been killed !
People like James Hunt/ Barry Sheene/Gerry Marshall etc will be remembered by their fans for their exploits off the track as well as on them, TV exposure and ads will make people remember them even more.
It can even work the other way round as people would have heard of "Eddie the Eagle"
Obviously if you are a keen F1 fan then "an icon" is subjective and possibly a driver who they have followed for years, even though they only won one WDC or none at all !