While the two have some divergence in what they are intended to solve for, grid-row-gap and grid-column-gap (or grid-gap) are the biggest day-to-day wins with grid. I had a fairly straightforward hack using negative margins and calc() to get spacing with flexbox, but the built-in support for it in grid makes it feel hacky and cumbersome to go back.
Grid's fr (fractional) units also make the old percentage-based format for responsive sizing feel unwieldy in comparison.
You get it. Grid-gap is so powerful and I can never go back to flexbox even for 1-dimensional stuff. My favorite is using minmax() to control responsive overflow.
Grid's fr (fractional) units also make the old percentage-based format for responsive sizing feel unwieldy in comparison.