In the extreme case that Obscura and Mullvad are forced to cooperate, you're right that this is the case. However, this is strictly (and much) less likely than a _single_ party being pressured or even a single party's infrastructure being hacked.

Another important thing to note: in our App, you can check your connected server’s public key against those listed on Mullvad’s server page, since we use the same servers as Mullvad's normal ones. It would be unheard of for a VPN provider (let alone a trustworthy one like Mullvad) to give their WireGuard private keys to a new partner.