You're right, the analysis is oversimplified.

I wanted to find out more about it, because a client of mine happens to be in a similar situation and is reconsidering their cloud strategy. Also, I'm quite familiar with 37signal's services and expected them to have done their homework on this.

Turns out they did. Found a lot more detail on their reasoning in a podcast of theirs in late 2022. I only read the transcript, which unfortunately may have been auto-generated since it seems to contains some errors. Still quite informative, though.

You can find the podcast here, if you're interested: