My vision isn't very good. The text becomes comfortable to read at around 175%-200% zoom level. The default size is so far outside that range that I have no qualms about describing it as unreadable, even if it's not literally true and I could read it with sufficient concentration.

Just to be clear, I don't think the problem is the tiny font size as such. It's the tiny size combined with gratuitously unscrollable and unscalable layout. It's a similar problem to many default themes for blogs disabling zooming on mobile browsers for no good reason. This got so bad that the Android browser sprouted an accessibility option to force zooming to always be enabled.