I think the difference here is more that I'm talking about the practical reality of today's display interfaces (both sides have a full frame in memory, typical

I think the difference here is more that I'm talking about the practical reality of today's display interfaces (both sides have a full frame in memory, typical overall latency is 5-50ms), whereas you're discussing what could be theoretically possible with dedicated emulation hardware that streams out an unbuffered HDMI signal and an HDMI-supporting CRT that operates similar to a modern VRR gaming display.