The interrobang only dates back to 1962, didn't actually appear in a typeface until 1965, and from what I've been able to find, it didn't start routinely appearing in typefaces as a distinct character until it become part of Unicode. So don't blame old typesetters -- blame the internet. :)
I don't see anything wrong with the interrobang, although I don't think I'd go out of my way to use it, simply because it calls rather undue attention to itself. I wouldn't say that about most other ligatures, even some relatively uncommon ones; I'm sure that most people read text in set in Chaparral, for instance, without ever noticing that "Th" is a ligature in that typeface, because it looks optically correct in the same way the near-universal "fi" and "fl" ligatures do.
For the record, I can't find any supporting evidence about the ordering of punctuation marks; both "?!" and "!?" are non-standard in formal English, and the advice I've seen online -- and in the Chicago Manual of Style I have on my bookshelf I just checked -- suggest that an "exclamatory question" just uses the exclamation point. It's just that "?!" is more common when it gets used. (A question mark comes after an ellipsis not because of punctuation priority, but simply because the "..." indicates elided words, but doesn't replace the terminating punctuation mark.)