Dude, that’s a really shitty take and this is why people that do care about security end up ignoring advice from anyone who thinks this way.
You’re in the camp of “don’t use condoms because they can break”.
If there's nothing to connect to, is there really an incoming connection?
You aren't in control of the contents of inbound packets, and NAT won't filter them to enforce anything about the destination IPs in them either.
Symmetric NAT 100% stops inbound unsolicited connections to the public IP. And using the public IP is the only way 99.999% can address you.
I implore you to write down (even if just for yourself) what the packet headers would be for you to get a packet from Starbucks WiFi to the device at your home at 192.168.0.5 that has made no egress connections.
You’ll quickly find what you’re suggesting is nonsense. port address translation requires an entry to function. It’s not some optional security feature. It’s required information to get the packet header rewritten to reach private devices.
> Symmetric NAT 100% stops inbound unsolicited connections to the public IP
No, it doesn't. If it did it wouldn't be possible for routers to accidentally make their web admin or UPnP interfaces available to the Internet.
It doesn't stop connections to your router, and it doesn't stop connections through your router either. It just plain doesn't stop connections, which is why it protects you from 0% of attackers.