The not cool parts just relate to any sort of hosted bridge. If you don't trust them with decrypting messages on their end, then don't give them your data - there are no bridges capable of doing that, anywhere.

So it really comes down to "trust someone else with your data, or host it yourself"; and if you're - understandably - frustrated with those options blame companies like WhatsApp or Discord that make it nigh impossible to integrate their services with outside networks.

Functionally, these bridges just forward your content to a library acting like a headless client - there's no way to encrypt that as the reverse engineered clients are not libraries and need to take raw input. You can't end to end encrypt it as the client is one of the "ends".

As an example, the WhatsApp bridge uses WhatsApp web as a backend, and has all the limitations of WA web.

As a result, I find the expectations to be a bit unrealistic.