Do any of those competitors actually have meaningfully better uptime?

From a societal level, having everything shut down at once is an issue. But if you only have one POS system targeting only one backend URL (and that backend has to be online for the POS to work) then cloudflare seems like one of the best choices

If the uptime provided by cloudflare isn't enough then the solution isn't a cloudflare competitor, it's the ability to operate offline (which many POS have, including for card purchases) or at least multiple backends with different DNS, CDN, server location etc.