I think you misunderstand how mesh VPNs work. Their primary purpose is as a control plane - introducing peers to each other so they can either communicate directly or via a relay (eg DERP) via per-node encryption. They should have no overhead compared to a single point to point encrypted tunnel like wireguard, because the “mesh” features are not in the data path.
The only real difference here is how the vpn product implements wireguard: userspace or kernel space, and how well tuned that implementation is. It might make sense to compare wireguard implementations, but (afaik) all are using one of several open source ones. Tailscale did some work to improve performance that they blogged about here https://tailscale.com/blog/more-throughput
Neither Nebula nor ZeroTier is based on Wireguard.
What they compare in the article are systems that provide some form of ACL, which is why bare Wireguard is not included. That means there are features in the data path that could have significant performance implications versus a simple tunnel. The impact of using ACL features isn't really a focus of the presented benchmarks, but they do mention a separate test of using iptables to bolt on access controls.
The only real difference here is how the vpn product implements wireguard: userspace or kernel space, and how well tuned that implementation is. It might make sense to compare wireguard implementations, but (afaik) all are using one of several open source ones. Tailscale did some work to improve performance that they blogged about here https://tailscale.com/blog/more-throughput