Neither were the first of their kind that I (or millions of others) used.
I'd used both CP/M and Apple DOS before MSDOS - neither were exactly niche products back then. And Altavista was pretty well established as the best search engine before the Google upstart appeared.
As for social media, Myspace had 100 million users in 2006 and wasn't passed in popularity by Facebook until a couple of years later.
All of these things were entrants into well established markets which had (at the time) heavyweight incumbents. They've all become vastly more successful than those incumbents, but that's not because they were inventing or even popularising a concept. These weren't obscure concepts that these people took mainstream, and there have been/will be other hugely successful entrepreneurs in every single one of these areas at some point.