I believe performance is situationally dependent, so it may or may not be faster, but it theoretically is. I personally choose wireguard over tailscale because it's one less 3rd party involved, not for potential performance increases.

I think you have a misunderstanding about wireguard clients.

As long as the server isn't behind a cgnat, a connection from the client to the server can be made. It does not matter if the client is behind a cgnat or not. If that were true, privacy vpns like proton and mullvad would not work.

That said, tailscale is easy to setup compared to a wireguard tunnel, but wireguard has potentially more performance because tailscale uses wireguard-go rather than wireguard kernel.

Yes it would. If wireguard is hosted in a vps, they can setup a client on their home network and mobile device, bypassing their home and isp nat.