Earlier quoted context omitted.
Is “SaaS” traditionally considered a niche like the others? The concept seems very broad as opposed to others like Fintech or Healthcare. I would consider a category like “APIs” to be overbroad, and SaaS seems to be similar. I’m very open to being wrong though.
SaaS is all over. I can think of 100 SaaS companies by me in Indiana, and I didn't look that hard. I think it's not an Astin niche...
Yes. By its very nature.
Plus, SaaS is more like a horizontal niche (though I would really call it a layer, with, e.g. shrink-wrapped software being another horizontal layer), while fintech, healthcare etc. are vertical layers[1]. In fact, the industry jargon term (outside of the narrow world of tech, at least), is "verticals". Ask any marketing guy. Verticals are usually defined by the business domain they apply to.
[1] E.g.: you can have a fintech SaaS and a healthcare shrinkwrapped app, and vice versa, and so on.