As other have pointed out, Tailscale and Netbird are much more than wrappers around Wireguard. ZeroTier does not use Wireguard and they have their own lightweight tunnels, which in their recent multi-threaded implementations are more performant but not as fast as Wireguard in my testing.

I don't think there's a direct way to integrate any of them into existing mesh networks, but I could be wrong.