Literally the only reason TLS uses certificates is to mitigate Man-in-the-Middle attacks.

Establishing a shared secret with another party over a public channel is not that hard (Diffie-helman, RSA). The hard part is to ensure the other party is who they say they are. Certificates tackle this by having a trusted party (CA) cryptographically bind the shared secret to an identity.

There are issues here, but if you can read and modify the traffic between my PC and the HN servers, you still won't be able to read and modify the traffic.