The cell borders example is misleading. The readability issue is not the cell borders themselves, the issue is that the borders are heavier weight than the text, and there’s no difference between the borders separating the row and column headers, and the borders separating the data rows and columns.
If your only choices for gridlines are “off” and “obnoxious”, “off” seems like a good choice. And for small tables, no borders works well. But for larger tables, finer lines (maybe in a lighter color or shade) can really improve the readability.
I remember as a kid, about 12, loaning my less-mathematically-astute younger brother $4, at 10% interest per day, compounded daily. I remember gloating about how much money he was going to owe me. I was going to be RICH, mwuahh hah hah!!
My Mom told that loan sharking was illegal, and my Dad told me that contracts with minors were not enforceable. My brother I think borrowed some money from one of his friends (on much more favorable terms), paid me back with one day’s interest, and never borrowed money from me again.