> [...] why would I trust some VPN provider any more than my ISP [...]

Of course, whether or not to use a VPN always depends on the specifics. (threat model, circumstances, VPN provider, etc.)

I am with the biggest telecoms provider in Germany, and I trust them about as far as I can throw them.

They are known for censoring their DNS servers, being opaque about government requests, and creating artificial bottlenecks to extort money from companies in order to avoid throttling.