Oh, that’s curious. I can reproduce the same thing: when I remove ~/.XCompose, the compose key does start working, with the default bindings. When I add back ~/.XCompose, with my custom bindings and no include directory, the default bindings go away but the custom bindings don’t work.
(BTW, is there an easier way to exit Weston than kill -9 $(pgrep weston | head -1)?)