It follows the rules alright. They’re just rules that have nothing to do with the original Greek.
Traditional English pronunciation of Latin – Wikipedia
In the middle of a word, a vowel followed by more than one consonant is short, as in Hermippe /hərˈmɪpiː/ hər-MIP-ee, while a vowel with no following consonant is long.
Hence, Hĕrmīone. (Long and short as in Modern English spelling: long i = [aj].)
Endings: … The first class consists of vowels alone, i.e. -a, -e, -æ, -i, -o, -u, -y. In this class, the vowels are generally long, but -a is always /ə/.
Hence, Hĕrmīonē.
Latin stress is predictable. It falls on the penultimate syllable when that is “heavy“, and on the antepenultimate syllable when the penult is “light”. … A syllable is “light” if it ends in a single short vowel.
Hence, Hĕr-mī´-o-nē.
However, when a vowel is followed by a single consonant (or by a cluster of p, t, c/k plus l, r) and then another vowel, it gets more complicated.
- If the syllable is unstressed, it is open, and the vowel is often reduced to schwa.
Hence, Hĕr-mī´-ŏ–nē, [hɜɹˈmajəniː]. As opposed to the Ancient Greek [hermiónɛː], or the Modern Greek [ermiˈoni].