> Only one peer is allowed to use 0.0.0.0/0 for AllowedIPs
This is simply incorrect. You can have two peers with the same AllowedIP; you just have to put them on separate interfaces (wg0 and wg1 for example). This is for exactly the same reason that a routing table can only have one default entry. If you want two default entries, make two routing tables.
> Yes but UI wise it presents itself as one
No, it doesn't present itself as one.
> since it’s acts as an interface
So does /dev/net/tun, which is definitely not a layer 2 interface either.