I was looking at rubygems.org at some of the more popular gems, and I see a bit of a mix, but there are a lot of >= x.y.z (including some ... and <= x.y.z). Definitely some ~> x.y.z and ~> x.y. But I’m not sure how it compares to hex packages usage. rails, of course, just ties each version to exact = x.y.z of it’s custom sub-dependencies (actioncable, actionpack, actionmailer, actionview, activestorage, etc…). Those sub-dependencies use a mix of >= and ~>.
Maybe an interesting project to gather data from the two and compare usage 
