I'm really puzzled by that statement.

RFC 4253(SSH Transport Layer Protocol)[1] says:

   It is expected that in most environments, only 2 round-trips will be needed for full key exchange, server authentication, service request, and acceptance notification of service request.  The worst case is 3 round-trips.

I've never experienced any issues w/ session initialization time. It should be affected by the configuration of both server and client.

[1]: https://datatracker.ietf.org/doc/html/rfc4253