I find https://rscss.io/ to be a really nice design philosophy that takes the best parts from BEM.
And agreed: it's easiest to just work directly with flexbox (and grid if you can drop IE11), and a set of design principles is really valuable to avoid spaghetti.
I don't mind hand-writing CSS for a small project, but I feel like once you've got a decent team, it ends up being duplicative and wasting a lot of time. How many times do you really need to style button/link and write out your 8px margins (or is it 6?) Sass solves this too, but simply applying classes is even easier and faster for me at least. I thought BEM was horrible when I first saw it, but once I used it, the productivity just feels like magic.
Vanilla CSS has custom properties[1] (which are more powerful then SASS variables) and there is a proposal for the `&` nested selector[2] which you can get with PostCSS[3]. All you are missing are mixins, but there is a PostCSS plugin for that[4].
Who's to say you can't use Sass variables _and_ CSS variables?
My current shop is moving to switch our sass color function `color.get()` to either dump hardcoded hex or a css variable usage based on a param. It currently just does hex.
Well, it was a response to the parents claim that “[w]riting actual CSS is the waste of time”.
You might be happy to learn that CSS color module 4[1] will add `lab()` and `lch()` color definitions and CSS color module 5[2] will add the `color-adjust` function as well as other goodies.
Once I discovered utility classes, I found it so much better than BEM or any derivatives of such. I don't want my styles to know what my components are, I want my components to use predefined styles.
I feel like utility classes and BEM go well together, though. BEM for sort of atoms/molecules (to use the lingo from the linked css-tricks page), and then utility classes to tweak the components, and to make components play nicely together (Fixing up margins, etc so things flow right and are the right size.)
I've moved on though, I learned flexbox and css grid and some atomic design principals as well as ABEM (https://css-tricks.com/abem-useful-adaptation-bem/) and I'm happy.