I would claim that most people that need a dedicated GPU for gaming are using steam

True but you said "If we are talking gaming (which by no means is a niche market), nvidia absolutely dominates the GPU market". So gaming in general which includes the massive number of casuals playing simple web games and that's what I was replying to. Gaming with dedicated GPU is a niche market compared to the sheer size of the overall PC market which has an installed base of literally billions of devices in use. So again: NVidia has no monopoly.