Earlier quoted context omitted.
RMS is wrong insofar as he believes that FOSS exclusively will result in more people having better software than if there is FOSS + ~FOSS.
The post in question makes no mention of FOSS exclusively resulting in better software than FOSS + non-FOSS. Are you just debating Stallman's generic platform here? Seems a bit off-topic to me...
[edit of first sentence for clarity]