I think most people don't use either shortcut, but that the ones who would use jsbin's shortcut are likely to use the browser shortcut. So it's not a great feature. I wouldn't call it terrible because it's only a problem for a small fraction of users.

Ace Editor is much worse, in that it overrides the Cmd+L key, on sites that have merely embedded it. https://github.com/ajaxorg/ace/issues/210 At least with JSBin, you might be able to get used to its overriding by noticing that you're on JSBin.