Again: The key difference is that in VS.Code the UI runs local, thus all UI interactions are "immediate" and there is no difference between local and remote operation. Yes, IO has latency, but where possible that is hidden by the UI (possible: saving a file happens without blocking UI; not possible: loading a file requires the file to be loaded .. but even then the UI can already prepare the window layout)
Thisnis very different form a system, where each keystroke and each menu action has to be transfered first, before the remote side can identify the needed UI update and send that back
Johannes's point was, I believe, that using VSCode remotely works fundamentally different than using apps remotely via X. I don't think he is confused about how X was designed.
Arguments to authority aren't appealing. Arguments from logic are. The fact is that X and VSCode's remote protocols are designed very differently, and in high-latency and high-jitter connections (and many low-bandwidth ones), VSCode's protocol is simply better.
Thisnis very different form a system, where each keystroke and each menu action has to be transfered first, before the remote side can identify the needed UI update and send that back