Are most people using PostCSS? Are a lot of front-end people married to JavaScript-specific tooling? Because Tailwind does all the same stuff and works anywhere.
I mean PostCSS is cool, but I don't see how it's actually better than alternative tools. It just makes CSS easier in one particular aspect, at the expense of others. Like pretty much all tools.
I agree, but what sets PostCSS apart from other tools is its forward compatibility. Which is a reason to opt for it for many people, including me.
At the end of the day most people will benefit from having vanilla CSS knowledge anyway regardless of any layer they prefer to use on top of it. SASS is such a layer as well as Tailwind. PostCSS is just tomorrow's CSS. It is to CSS what Babel is to Javascript. So using PostCSS instead of SASS is comparable to using Babel instead of for example CoffeeScript.
If one deems that tomorrow's CSS as it currently stands is advanced enough to handle "big, engineered stylesheets", then PostCSS may well be all they need. But I don't think there is a single right answer here.
Sounds like SASS isn't obsolete if that is the case. Saying something is obsolete implies there is _zero_ reason to use it over some other solution.