What's the point of requiring the control plane to be locked down to authorized networks (IP address ranges)? Isn't Google responsible for DDoS protection, enforcing authentication controls (i.e. logging in with a Google account in the right Google group), patching the control plane ASAP for any security vulnerabilities?
If you have a VPN, if you have heavy-duty network monitoring on your VPN endpoint, sure, limit it to the VPN. For the rest of us? Is every startup running GKE without heavy-duty VPN / network monitoring fundamentally insecure? That doesn't sound right to me. Security is supposed to be a spectrum, and it seems like black-and-white automated config checkers like these are more likely to provoke arguments internally ("but the tool said it's bad!!") than to help reach a nuanced understanding of why tradeoffs are made. No?