In my philosophy some of the "umbrella tags" are useful for the less-frequent tags. In particular, this would be an edit I'd reject (but not reverse).
The abstract-algebra is relevant for every question which is about group theory, ring theory, modules, fields, Galois theory, and more and more. It's a huge topic, and it clearly covers a lot more than group-theory.
Some of the subjects have well-represented tags here, like the group theory tag with over 6,000 questions and nearly 400 followers. However tags like rngs have vastly less exposure to the main page. So it is useful to have an umbrella tag like abstract-algebra or ring-theory available with it.
In conclusion, my argument is that abstract-algebra is usually for increasing the exposure of a question whose other tags are indeed relevant to abstract algebra, but have less followers; and rarely for questions about "general" abstract algebra. Of course group-theory isn't such tag.