Here’s the thing: This chart NEEDS gridlines. I’ve said this before but I find this anti-gridline trend so common that I need to address this topic explicitly.
The *medium gray not black* gridlines are necessary because I do not have data labels on every one of the dots in the chart.
A quick reminder is that even Edward Tufte (a key proponent of the “gridlines are bad” school) doesn’t hate all gridlines. Subtlety is key with them: they should be there when you need them but easily ignored when you don’t.