AFAIK it worked a lot better back then because X programs sent basic drawing instructions, so messages were tiny. I'm pretty sure most of them send images over the wire now for the whole window, like VNC or what have you, thanks to all the fancy eye-candy and extra layers we've added.

That's still a stupid way of doing it. What they should be doing is caching pixmap atlases server side and sending draw requests to draw subsets of those. If they send an entire image over the wire for each frame draw, it's purely due to developer laziness.

Also, with "flat design", suddenly libXaw is on the cutting edge of UI look and feel again...

Yes, they do that. But they often use Xshm to upload those pictures to the display server, and that still means sending them to the peer for server-side blitting.

Further more, by using TCP/X11 for the wire protocol, any dropped packets have to be retransmitted before you can update unrelated portions of the display because it requires in-order processing by design.

This is why high-quality, high-frame-rate remote displays never use that design.

Developers don't get to see what is going on, everything is hidden in multiple layers of libraries, it isn't down to laziness.

Someone had to write the libraries!