People tend to sometimes get passionate about their grids. Some prefer 12 columns, others prefer 16 or 24, others are happy with 6 and others hate grids.
A grid would be beneficial only if not enforced. I can see myself using it if I can choose how many columns I want - if any.
If my design requires me to do golden ratios for some blocks then a grid would prevent me from being able to create what I have in mind. Instead if freeing me it would trap me. And that's not what WordPress should be like...

If a grid gets added the user should be able to
1. Define globally if they want a grid, how many columns they want their grid to be and whether they want gaps between columns and how large these gaps should be
2. Be able to disable, or even override the global grid in a block.

And of course if users do get the ability to define their grids, gaps etc under no circumstances should we enforce the use of pixels by implementing slider/range or numeric controls for the size selection etc. I like em units, others like % and then there's the occasional vw etc.

A grid is beneficial if it's by choice and fits the user's needs. But we can't know what those needs may be, so we'll need to be versatile and not enforce what we deem as "reasonable".