First of all, starting off an argument or a debate with the term 'pandering to legions of Seph fanboys' is hardly going to win you over any aid or support. Second, there is a reason why respected sites such as Wikipedia, Gamefaqs, the Omega Guide, the FFVII game itself, and even Advent Children state that Sephiroth is the true villain of FFVII. You can cry and whine about it, and the fact that he is loved as a villain so much, but nothing changes that fact. The only grey area is exactly how he accomplished this during the game, and many people and sites believe differently. But the one fact remains, Sephiroth was the main villain of the game.

In the time of the Cetra, Jenova was a powerful alien entity. She came from another world looking to destroy the Planet, and she was eventually stopped by the Cetra. During this time, we know that she has certain abilities - like changing her shape and form. By the time FFVII actually started, Jenova was in a completely dormant state. Now, the Jenova Reunion is a concept where all of Jenova's cells will one day reunite and she will be reborn, however, locked in stasis (and without a head - which we'll get to in a moment), there was no expanding will from her form to begin this process.

A few years back in the Nibelheim incident, Cloud defeated Sephiroth, and he fell into the Lifestream along with Jenova's head. As explained in the Temple of the Ancients segment, Sephiroth spent that time 'traversing the lifestream and learning the powers of the ancients'. What power do the ancients, or Cetra as they are also known, possess? Well, we know that they can commune with the Planet, that it is their power contained within Materia, and more importantly, we know that they can leave behind their consciousness in a physical form as displayed by the Cetra forms left behind to guard the Temple. The only reason that they could no longer speak, as explained by Aeris, is because so many years have passed and they have forgotten how.

So, Sephiroth has the power to project himself and he has Jenova's head. As we know, Sephiroth's dying body eventually landed in the Northern Crater. Aside from learning about the ancient's power, he also learned about his 'Mother' Jenova and her true goal. She wanted to destroy the Planet. Advent Children even furthered this as Sephiroth explained that Jenova had wanted to ride the Planet's rotten carcass to other worlds in order to destroy. That was what the original Jenova Reunion was all about. However, we know that this was not what Sephiroth himself had planned.

Going back a little, we know that Jenova's cells all pull together from her will in order to reform herself, however, from all displays and explanations in the game, Sephiroth's will was far too powerful for this, and he ended up manipulating her. Instead of her reunion, Sephiroth was going to use the reunion of her cells, and more importantly, the calling of Meteor, to bring the Planet to near destruction. This very act would cause a massive surge in the Lifestream - right at the Northern Crater - which, if you remember, is exactly where Sephiroth is. He was going to use this chance to absorb his spirit into the Lifestream and 'become a God'. This was never Jenova's intention, or thought - she just wanted to destroy the Planet, and again fuels the reason why Sephiroth himself was in control.

Right. Going back to the Jenova changing her shape and form this is shown during the game. On three seperate occassions, Sephiroth flies away from the group and leaves behind a piece of Jenova for them to fight (which transforms it's shape into Life, Death and Rebirth).

Speaking of Jenova Rebirth, there is a very good reason for this last name of her. Many believe that she used the partial cells of those gathered in the Northern Crater to create a partial rebirth of herself. That was her final act and battle in the game, after which, her role is moved on to Advent Children (as since the battle took place deep in the Northern Crater) her cells got distributed amongst the Lifestream, causing the Geostigma during the film.

The final, undeniable argument, is that the final boss of the game is Sephiroth. The group fight him as a whole, and then, Cloud fights a final battle (whether you believe it was a mental or a physical one) with him.

So there you have it, pretty strong evidence to counter what you say. Either way, if so many people, and the producer and script writer of the game, say that Sephiroth is the main villain, then you'll just have to deal with it I'm afraid...