The main drawback for those things is that you cannot parameterize them, which is a bummer if you've created a shape that you might want to vary in ways that a transform cannot easily do.
For styling purposes, yes, CSS allows a lot and things like currentColor enable you to at least have colors and styling dynamic when instancing symbols. But things like parametric shapes don't work without scripting, which is a bummer, since in many other places SVG is very amenable to handwriting with a lot of cool features. Just not with a lot of abstraction options.
