I can see that Gillean would have a hard G, and that if one wanted it to have three syllables in English one would probably play safe and use the -ian version, thus also avoiding confusion with surnames like Gilham.
I can't recall ever seeing or hearing about a male
Gillian. I've known some
Julian people, and of course etymologically
Julian was unisex in the Middle Ages and ga e rise to
Gillian and
Jillian. I'd expect a girl
Gillian and a boy
Julian. But hard-G
Gillian would be a natural spelling pronunciation.
When I was in my fifth year of primary school, a new girl named
Gillian joined the class and our teacher, who I think used to speak two European languages at home, English certainly and perhaps one of the Scandinavian ones, asked her how it was pronounced. The child innocently explained that it was actually
Gillian with a J sound, but that her mother sometimes used the hard G sound when they were out, to impress people!
I also like soft-G
Gillian enough to use!