Buffy never saved the world in six or seven....she was stuck in a hole for S6 and S7 Wolfram Hart saved the world by giving Angel the amulet which he intended to wear in Chosen, but Buffy sent him away to start a 2nd Front , the only people who had any idea what the amulet would do was Wolfram and Hart , Spike / Buffy didn't so when Spike put it on he had no idea it would do ? So I don't understand the big Bomb ?I certainly would have liked to see more slayer action... but then again, I really would have liked to see them do the spell before they went down into the hole... and maybe gather several hundred slayers around the school. I bet you there were a bunch of undiscovered potential slayers in CA, OR and WA alone...
I don't have a problem with the idea of Spike's soul burning out the enemy. Seems oddly appropriate that a vampire's soul should kill all the vampires... and it brings him full circle. Spike's humanity is why he joined forces with Buffy against Angel and Dru the first time... and now he's got his human soul and the fullness of humanity, at least from a spiritual standpoint.
Spike is only there because of Buffy's action, therefore, I credit the win to her column anyway. General's don't shoot the big bomb, they just decide how and where to deploy it. They still count as winning the war. She is the one who insisted in keeping him around, saved him and deployed him in battle. So it's not 'man power' saving the 'little woman'. It's the 'little woman' figuring out how to use her big guns. Willow. Spike. The potentials. And SHE wins.
You don't have to be the only one on the field to win the war. In fact, in modern wars, the general and the president pretty much aren't ever in the middle of the battle.
Without BUFFY, there's no Willow the powerful witch. Willow dies in season one. Without Buffy, there's no Angel the redeemed with an amulet... he goes on wandering lost in the wilderness. Without Buffy Spike either gets killed by some slayer or goes on being evil. Without Buffy, the potentials don't survive, much less become slayers who help save the world.
Everyone in that building who fought that battle was there because of BUFFY.
Chosen wasn't perfect but it was pretty good. Given the huge missteps of season seven, it's actually a pretty good 'save'.
But there definitely could have been a bigger role for the new slayers.