The "Obscura and Mullvad" argument actually makes sense. Having a company outside of EU jurisdiction makes it hard for both layers to be compromised at the same time.

Another question: How does the Obscura client get the Mullvad exit server’s public key? Are they hardcoded at compile time, fetched from Mullvad's server, or fetched from Obscura's server?

The latter seems to be dangerous if there isn't some kind of signature verification done on the client side before using the key.