You're definitely shifting your attack surface towards the CA, but in doing so you've (probably) given yourself a lot of additional control over the weakest lin

You're definitely shifting your attack surface towards the CA, but in doing so you've (probably) given yourself a lot of additional control over the weakest link in your system. With cleartext, vulnerabilities tend to range from simple things like "find the switch, plug in, sniff traffic over the wire" to slightly more complex, but still viable things like "sniff wifi traffic now, worry about cracking WPA-2 later". Your typical TLS certificate is going to be more robust than your typical consumer / prosumer LAN security, and you typically have better tools (SSH certificates, 2FA, encryption at rest, etc, etc) for locking down a machine running a CA than network gear you either don't control or bought from a consumer-focused vendor. Its a typical example of defense-in-depth. Hopefully your network is trustworthy, but if for whatever reason it becomes insecure/vulnerable you now have genuine encryption between client and server at application layer.