OPs method would allow for remoting into your home network without port forwarding, since home network would establish a connection to the 'bounce' node, which would facilitate communication between the 3rd WG client
For minimal setup, zerotier looks like the winner.
Same thing for a router configuration to accept inbound wireguard requests on a home network with dyndns. You set it up once and are done.
I see the benefit of the bounce server if you operate a network in an environment where you don't have the ability to control the router config; however, when you do have the ability to update firewall/router config, then I'd prefer just setting up a domain name and avoid the dependency on a third party server.
But you do not seem to be getting that the use of nftables, for the open-network bounce server, is wholly optional.
I am not sure the nftables configuration I have is right... It might permit using my bounce server to forward packets that then appear to come from it, if they happen to mention the right port. I would welcome advice.
After further investigation, I have discovered that dyndns would not solve my problem, because the firewall at one end is especially picky; even zerotier and tailscale admit (grudgingly) that they use bounce servers for such clients.