SSH does it's own flow control, and with HPN-SSH it is much better.
Also, if your connection to the VPN host is quite good, then the TCP-over-TCP issue does not apply as much. The bad cases happen when that connection has packet loss.
Also, if your connection to the VPN host is quite good, then the TCP-over-TCP issue does not apply as much. The bad cases happen when that connection has packet loss.