fewer has no opposite like less-more

Everybody learns in grammar class that when one is speaking of countable things, "fewer" must be used, whereas "less" is reserved for uncountable quantities, e.g.: less traffic, but fewer cars.

Yet there is no such equivalent pairing for more, thus perhaps proving that Ludwig Mies van der Rohe was wrong, and in fact more is more. (See less is more)

This is a grammarian mistake. In English, there are two words of interest to this node: much and many. Both of them have the same comparative - more, and the the same superlative - most. A parallel situation exists in some languages, and others have completely distinct word-sets for the concepts of discrete quantity and continuous quantity.