That's true.

The problem I see with that is that PuTTY doesn't really have a need for high performance as much as WinSCP does. And has PuTTY seen any updates the past 3 years? Is there any development being done at all on PuTTY?

Thanks for your hint. Though WinSCP uses SSH implementation from PuTTY, so unless they implement it, it won't get into WinSCP.

See also: https://www.psc.edu/hpn-ssh-home/hpn-ssh-faq/

I use WinSCP a lot on LAN, and reach nowhere near wire speeds. And even though I have a 4-core machine, only 1 core is being used by WinSCP. If the encryption was spread over multiple threads (like hpn-ssh does) things would be a bit faster.