And yes, it does break MITM use cases, for example on Chrome: https://httptoolkit.com/blog/chrome-android-certificate-tran...
I don't currently MITM my LAN but my general attitude is that if something won't accept my own root certificate from the store then it's broken, disrespecting my rights, and I want nothing to do with it. Trust decisions are up to me, not some third party.
The default should be to reject certificates which aren't being logged, and if you as a user or corporation have a reason to use private certificates, you just configure your computer to do that. Which fully protects against the risk of normal CAs signing fraudulent certificates.