They could've called him "Wandering Soul" which is what it supposedly translates to, or "Soul". The character who called him "Kevin" didn't bother to figure out the name's meaning and went with with something that started and ended the same.
Not exactly sure on the pronunciation of the Greek, but 3-4 syllables isn't that bad. The "i" is really the only bit that's tripping me up. I don't know enough about Greek to say what the conventions on dimunitives or shortened forms are, either. Probably the best place to start if you wanted to shorten the name. Or the character could have some sort of snappier nickname. Doesn't have to, though. The main character in Perdido Street Station is named Grimnebulin and Mieville gives him no snappy nickname. I don't recall the name being a problem, but then it's easily pronounced and rolls off the tongue.
I think it's up to the author to abbreviate a name or not. It's up to the setting, the character, the culture to which the character live in, and how much the author feels about typing that name out over and over again whether that name would be shortened or not.
For example, I've a character named Nicodemus. It not really long but long enough that I don't want to type it out every time I need to use his name. I just use his abbreviated name, Nico. He tells everyone to call him Nico. It's what his sisters and his father call him. There are a few instances when he is referred to as Nicodemus for formal reasons, to get his attention, and one character who uses his full name as means to show respect. I figure if the character wants others to call him Nico, and I introduce him as Nico to the readers, that is what I will continue to write in the narration.
I was told you should pick a name to write and stick with it unless there is a reason why someone else refers them by another.
Type it out in full every time, first, last, middle, clan, cognomen, and dynastic number. Can't be too careful about nomenclature, after all, and nothing says ACTION like spending half a paragraph just on the subject of a sentence.
I was once at a SF convention waiting for a reading from a particular author I was interested in. The author who had the slot before hers didn't understand that he'd been allocated only a half hour, so I had to suffer through a bit of his "Lovecraftian" story before staff cleared the situation up. For some reason, his POV character was always referred to by first and last name. Lovecraft never did this himself, so I have no idea why this guy thought he should do it in a pastiche, but he seemed to think it important because he didn't even shorten it as he read. The story was boring for other reasons -- he had used up a full half hour and hadn't even gotten to the horror part yet -- but this certainly didn't help.
I'm confused as to what sort of person thinks everyone wants to hear their story read out loud unless explicitly asked to do so. Clearly the same person who thinks his readers will forget who the character is if they only go by one name.
He was explicitly asked, in a way. It was a scheduled room for author readings. Presumably, those who showed up for them knew what they were in for. I think even his audience was tired of it, though. He got no support from them when staff asked him to pack it in.