This isn't about making things public, just resistant to tampering and sniffing. Yes if you want to connect networks together then wireguard is a good choice.
If your devices are already on the same network and instead you close down the firewall and you move everything into wireguard you've just moved your problem.
If your devices are already on the same network and instead you close down the firewall and you move everything into wireguard you've just moved your problem.