It's rarely beneficial to compress to one single file, but I completely agree that the way they are doing it it very inefficient, especially spamming the @import notation.
Not sure what you mean by "rarely beneficial to compress to one single file".
But in multiple situations I have seen significant web load performance improvements when the number of discrete files being loaded is reduced - merge all JS into one file, all CSS into another and sprite images. This is due to HTTP 2-connection rule.
But in multiple situations I have seen significant web load performance improvements when the number of discrete files being loaded is reduced - merge all JS into one file, all CSS into another and sprite images. This is due to HTTP 2-connection rule.