Do you really need to spend the time (and maybe money) for a second host just because your current one might go down for an hour? There's probably a point at which you might rightly consider it, but I doubt many people are legitimately at that threshold. Especially given I don't even remember the last time Netlify had this issue.

Doing it yourself qualifies as "a single expert is still a single point of failure". A single vendor at least has some levels of staffing and redundancy that I nor my company can match.