Well, for starters, tftp is the wrong thing for local file transfers if you want it to be fast. The only reason its still around is because its simple and offer the only file transfer protocol that is built into the firmware of the network card.
You read that right, its a simple file transfer protocol built into every network card made in the last couple decades.
Your best bet for file transfer is probably something like a WebDAV server. Which next cloud can handle for you. You can just enable normal WebDAV on something like httpd but then you gotta handle authentication yourself. (Or allow local and connect with VPN)
Yes, WebDAV will max your local connection. Its generally not the encryption that makes ssh slow but the fact that it is designed to give real time terminal feedback. In order for you to see each letter typed in an ssh session, the buffers are really small and it intentionally sends a tone of small packets. Great for single characters bad for large file transfer.
Its OK here and then when you need to push a config file or something but moving large files is not really what its designed for and consequently, it sucks.