Lora's Supercharger-problem fishing expedition led me to realize something.
Probably the most common Supercharger problem I see reported isn't that chargers (let alone whole stations) are down, but rather, that charge speeds are subpar. While there can be many causes for this, including in the vehicle itself, one common cause (when all chargers are showing the same problem for all vehicles) can be simply that the feed to the station cannot supply enough power.
But Tesla is planning to switch to the use of Powerpack-backed Superchargers. In theory, this entire class of problems should disappear when Tesla does this.