The pivotal work (with rtm and trevorj!) was Viaweb. Without that he would not have been able to start YC.
Also I presume he had substantial help in starting YC.
Many successful people like Bechtolsheim and Khosla go into the VC business. Still these two would probably list Sun as their major work.
The OSS contributor comment still applies: In the technology business one would need to go into the league of companies like Intel to even start comparing the wealth generated by companies vs. the wealth generated by OSS.