Since the beginning, iPhone keyboard is wrong in entering a character first, háček second. It has been the other way around on typewriters and then computers for decades. Then some smart guy at apple thought he knows better. One of those never-fixed-bugs.
Wait, really? I thought "dead keys" being diacritics prefixes, not suffixes, was pretty universal. At least that's how it works with ^, ´, and ` on macOS for me.