Currently ordinal scales default to round = true, which is why the bars disappear if there are too many bars (for a given width). Perhaps defaulting to false would be less surprising, though it would also mean uglier bars by default, or writing more code in the common case. Another option would be an “auto” round setting, which rounds but only if the computed bandwidth would be >= 1px.

Exactly. I think this exercise shows that some of the defaults tend to break charts with tiny dimensions—but it doesn't mean they're bad defaults in large dimensions. But it would be a plus if we detected when they become an issue and switched to better solutions in those cases.

Updated Plot and you don’t need to specify y for a 1-dimensional bar anymore.