iirc spiped uses TLS/OpenSSL for securing the connection, the symmetric key avoids the key-exchange and worrying about certificates, and therefore is better capable of efficiently using the connection than SSH by itself.

Because it's much simpler it's also a good way to expose a system to the internet, although Wireguard with a PSK is a very similar and possibly superior solution.

I'm presuming this is pretty similar to https://www.stunnel.org

We would use stunnel rather than SSH for non-interactive usages. Having an active stunnel running all the time is safer than requiring a full SSH session being active.