Probably not. They could mesh together pretty well, actually. I think the point that I really don't agree with in Hammer's theory is that I find pre-Nibel!Sephiroth and post-Nibel!Sephiroth to be noticeably different. I know that's subjective, though. Pre!Seph doesn't come off as someone that's arrogant or carries a superiority complex. Confident and sure of himself? Yes, I can see that. But that doesn't automatically come shipped with a "better than you, nya" attitude in the box.
Ok. Here's the trick right. We don't see any other character interaction from pre crazy Seph aside from Nibleheim in ff7. I felt Sephiroth was handled poorly in CC. So I'm just gonna ignore CC in that regard aside from a few points.
So I came up with another solution. You say Sephiroth doesn't enjoy the fame or the power? Then why does he dress the way he does. Why does he keep the long hair to let every person in the area know that there standing in front of possibly the most famous person on earth at that moment in time? All he has to do is.... SNIP SNIP.... and bam. Then no one knows who he is if he puts on the standard issue SOLDIER helmet.
One of the tricks alot of people forget is that Square started switching from telling you everything about a character to strongly implying via the unspoken word and various minor details about a character. Let's see how Sephiroth looks factor into his character then shall we? We're gonna be judging a book based on the cover today for the record.
Before you go this is an anime character.... take a look at angeal. They purposefully have him wearing the standard uniform unlike the bondage gear and a trenchcoat Seph and Genesis wear just to show he is humble. This means clothing is in fact a character statement.
http://finalfantasy.wikia.com/wiki/SOLDIER
Here's a link to a bunch of images and some art of some SOLDIERS.
http://finalfantasy.wikia.com/wiki/File:Sephiroth_Nomura_art.jpg
And there's Sephiroth. I know this is crazy seph but it's a good pic of his whole outfit.
Looks at the differences between his outfit and there's. He wears a large black trenchcoat and doesn't cover his chest. A more humble man wouldn't wear such clothes. He'd wear the standard 1st Uniform AND COVER HIS CHEST. The armored pads on his shoulders are meant to demote status more than being actually protective of his body. It's similar to a samurai's armor in some ways or the old outfits famous generals used to wear.
Hell the trenchcoat could be grabbed in the middle of battle from behind and he could be stabbed easily so in no way is it tactically efficient. Also... leather is incredibly uncomfortable in the heat. Finally though and this is possibly the most damning of them all: It shows his lack of respect for those beneath him.
A officer is supposed to be the best dressed in the squad, taking the military rule book to heart. He recognizes that in order to have discipline you must have unity. By forcing everyone to wear the same outfit this reinforces the philosophy that you are part of a squad and you must act accordingly on there behalf. Sephiroth takes a giant stinking shit on this and chooses to stand aside.
No one is forcing Sephiroth to wear this outfit. He could easily be wearing the standard uniform. He is purposefully choosing to stand out from the rest of his squad as a war hero.
I don't think I need to point out that Sephiroth was the only guy with long silver hair in ff7 originally. It's an iconic trait of his sure. But it also shows how arrogant he is. First let's talk about how it could negatively effect him in combat.
1. A strong gust of wind could temporarily blind him. This could allow him to be surprised in battle.
2. Somebody from behind could grab his hair and pull! Sure he's a uber soldier but he ain't invincible as Cloud shows us. This could get annoying and painful really quickly. They could even stab him or shoot him whiles he's trying to turn around or stab them with his giant phallic symbol THAT IS NOT DESIGNED FOR CLOSE RANGE COMBAT IN ANY WAY, SHAPE, OR FORM!
3. He stands out. I'd have every sniper in Wutai trained to aim for silver and mako-green if I were Lord Godo. It's only a matter of time until somebody takes his sorry ass down.
Now Sephiroth is basically superman so none of these are really that bad for him so let's look at the social ramifications caused by his hair.
1. He stands out. COMPLETELY STANDS OUT! No way is he going out in public without everyone staring at him. This must mean he doesn't mind his fame.
2. He's a SOLDIER. Look at the rest of the members of SOLDIER who aren't pretty boys. They were helmets. And they don't have hair sticking out from underneath the helmet. This must mean regulatory short hair. Sephiroth and several of the other stronger SOLDIERS show a disdain for rules and regulations with there long hair. You could even say Sephiroth inspired all the rest to have long hair.
Sephiroth is an officer and this means that as such he is supposed to be the embodiment of rules and regulations on top of the best man in his unit. This shows his utter disdain for the rules or the benefits from having shorter hair. It also shows his lack of respect for those working beneath him like I said above.
Last notice the giant sword he is holding. It's famous because no one else could wield it due to the size, weight, and shape of the sword. I always wondered how it came to be in his possession. Either way ... it's famous and adds to the legend that is Sephiroth. Even after he is crazy it is easily his most treasured belonging. Sure there's no bond like the one between a man and his weapon. But you have to wonder if Sephiroth didn't purposefully pick this for a weapon just to show how much better he is than the rest. Was he drawn to it because of it's fame for no one else being capable of wielding it... like some sort of sword in the stone?
Anyway, that about covers it up. I think taking his uniform into account we can easily say Sephiroth was a pretty arrogant individual prior to nibleheim.