If you mean CSS Grid, and you can afford to target only modern browsers (with usable fallback CSS for the others) then you're good to go right now. Even Edge is working on bringing their implementation up to the spec right now[2].
I agree with your other points too. CSS frameworks don't bring that much, and end up clouding your ability to write and understand raw css IMO.
[1] http://caniuse.com/#search=grid [2] https://wpdev.uservoice.com/forums/257854-microsoft-edge-dev...
Consider stuff like wordpress, and other large programs that need an easy to re-use styling language. When you use something like bootstrap, and others know bootstrap, then you're making it easier for you and your customers down the line to build on something.
You can always write your own thing, and in many cases this will work, but then someone else is going to have to learn all of the quirks of your system before they can get up to speed and start using it at scale.
- "The Grid", which at this point has migrated to the browsers with Flexbox and (soon) Flex Grids
- A pretty skin replacing the browsers' default rendering of elements. These have improved, albeit only slightly. CSS has also become easier and you can easily do this yourself in 50 lines or so
- Fixing browser bugs/inconsistencies, which have diminished to a fraction of where we used to be
- "Components", which may the last remaining use case, but which have also become much easier to do yourself due to sane grid layouts