Technically Estinien doesn't have a 'style'. He just doesn't cut it because he's lazy, so he got a special 'overgrown' edition of the longer hairstyles favored by Ishgardian Elezen.

Those don't typically have bangs so I'm wondering if one day he just got impatient and cut out a window in his hair. He's also got random shorter chunks all over the back. I like to pretend he has split ends

I think Zenos's hair is specially modeled so the bits that go down his front don't clip through his gigantic chestplate. Estinien's is sort of modeled like that but with less care so it does end up clipping since he has full range of motion and currently wears armor that sticks out in random directions. (See screenshot earlier in thread)