Ok -- by perusing the log I figured it out ...

In the past, .XWinrc names of files such as "xterm"
worked just fine. Apparently something changed about
the PATH used, and "xterm" was not being found. When
I write /usr/bin/xterm, it starts up. You can see the
first case and the second in the attached log file.

So, I think xlaunch is ok, but this was a surprising
difference :-) ...

Regards -- Eliot Moss