Jack Shedd says
CSS makes certain things remarkably easy. But there is a class of design problems that are nearly insurmountably hard due to poor design decisions within CSS.
Which may be true. But I’d posit to say that tables (catch his link) are not the answer.
In many cases, a more versatile system is going to be slower for the particular case that a simple system is built for. That doesn’t mean the versatile system is broken.
Having said this, I would like to read some good criticism of CSS. I haven’t kept up with it for several years and I think it makes an excellent model for sorting out a successor to LaTeX.