These three types of characters—word glyphs, diacritics, and letter sequence glyphs—constitute nearly the whole system. There are only a couple other minor additions and flourishes, like eg the reintroduction of the medial s, ſ.
It's certainly true that the system has obeyed something of a maximalist principle, at least along one or two dimensions. That is, if there's a rule that would be useful in saving space, character count or time, or consonant and aesthetically pleasing, then it's worth it to add it to the set. There is no value in keeping the total number of glyphs down.