actually, both HTTPS and WebSocket over TLS (wss://) require a TLS handshake, so it's not like you're constantly doing that after you've loaded the page, but HTTP request/response header sizes could def be a concern.
SSL Session Reuse needs to be configured as well, otherwise every single request will have to perform a new handshake, independently of keepalive.
In practice I've always observed HTTPS requests to take at least twice as long compared to a back and forth through a websocket, even when SSR and keepalive are enabled. I don't know if having both theorically allows for single-roundtrip HTTPS requests.
