Agreed, which is why I specifically didn't refer to the TimescaleDB TSL license as "OSS".

Then maybe open source definition should update as new ways to exploit it have been found?

Agreed, but I think there would be big pushback from OSS proponents - in theory changes like this are diametrically opposed to the "No Discrimination Against Fields of Endeavor" tenent.

The problem of big cloud providers ripping off OSS works is a new one, but it is explicitly allowed by OSS licenses - really not sure what a "good" solution is here, but personally I like the route TimescaleDB has gone down.

I don't think it is a new problem, there have been people offering Apache servers as a service for a long time. Same for PHP, Wordpress and myriad other open source projects.