Narrowing the bars is not reducing non-data ink ratio imo and against the spirit. The bars are the data. And they therefore should be maximally visible, the same way that you BOLD text (make it thicker) that you want to emphasize rather than thin it to "reduce non-message ink ratio."

For the width of the bar there is practically speaking a middle ground that uses thick bars but not too thick/close together such that it harms legibility.