I found that setting (customize-set-variable 'tramp-use-connection-share nil) made things "just work" with my .ssh config (the documentation for that variable s

I found that setting (customize-set-variable 'tramp-use-connection-share nil) made things "just work" with my .ssh config (the documentation for that variable seems to imply this is expected). If you still want connection sharing, you'll have to set it in your .ssh config, but it works without it.