Eh. I disagree. It's not like Sephiroth in Nibelhiem was at the same level of obsession and insanity as he was afterwards.
No, Nibelhiem-Sephiroth is a far cry from Sephiroth in FF7 proper, but he also acts very little like himself in CC/BC up until that point. He's a fairly nice guy, though obviously aloof. He knows he's different from normal people and even other SOLDIERs, but he still goes about his business like he's any other person on the planet and just tries to not think about it. Compare this to Sephiroth in the reactor -- he's quite the arrogant prick, to put it simply. There's talk about traitors and Ancients and taking over the planet with his mother because he's her chosen one. By this point, even though the crazy-seeds only just sprouted, he's already put himself on a pedastal above everyone else. The rest of the humans can go pick shit with the chickens. This is an attitude that pre-reactor Seph did not carry.
The problem with this is that this line of thinking takes away from Sephiroth and Cloud's dynamic.
Which is why Cloud's rank and mental disposition (he's insecure and until the end of FF7 somewhat weak-willed) plays so much of a factor in that very dynamic, which is what we're trying to stress.
I wasn't meaning FF7 or the compilation as a whole, I was more referring to the Reactor Incident by itself. As I said above, Sephiroth (in the reactor incident) thinks he's above the normal human race. This would have made a defeat by any human, SOLDIER or trooper, to be disgraceful, even if with a slightly different severity, because they're all worthless traitors.
Also, if Zack defeated Seph in the reactor, Sephiroth would still have no clue that Cloud even existed, because Cloud only stepped in because Zack failed. There would be
no dynamic for Cloud and Sephiroth to even
have. Sephiroth would have turned his anger towards Zack because
Zack was the one that killed him.