Buffy's been seen to take on four slayers at once, beat them all soundly, and not taking a single hit. There's practice and then there's that. 🙂
Exactly like Blaze said, that shows skill not better strenght.
4 slayers is a LOT of strength, by your suggestion if Buffy beat them cuz she's stronger, she'd be verging on superhero like strength.
She beat 4 slayers because she has 7+ years on them, and they have like less than a year.
Also, Geneive was unusually strong (she killed a slayer with one blow) yet both Buffy and Faith took her down no sweat. (Faith was trying to break up the fight and save Buffy from...Rondin? I think- but Buffy had already completely floored Gene, and then Faith herself was holding back and trying to reason with Gene all the way through their fight- then killed her by accident.)
I dont know how you define "no sweat" but Buffy and Geneive went blow for blow, Buffy didn't dominate the fight between them, same for Faith. Faith is battered and bruised by the end of their fight, she has more control in the fight, but if you look at the panels it's her skill that lets her move around Geneive, she isn't kicking the crap out of her, and the fact she killed her by mistake means Faith had to put effort into fighting her, if she'd been dominating her she wouldn't have accidentally killed her.
It's basically unclear whether their powers (which come from the scythe- a mythic slayer weapon) are equivilent to the Shadowmen's 'you now have a demon's essence empowering you now' spell.
Well no it's the reverse. There's nothing to suggest their powers aren't equivilent.
It was the same way when we say Buffy fight Kendra, and when she fought Faith. Buffy didn't dominate those fights, she went blow for blow, but she was still a better fighter.
I get what you mean about it being unclear, but for me thats like that saying "you hear hoof beats you think Horse not Zebra"
It makes perfect sense that Buffy and Faith would be better than the newer slayers just given their experience.
And again, the episode does say what Willows spell does:
"In every generation, one slayer is born... because a bunch of men who died thousands of years ago made up that rule. They were powerful men. This woman (points to Willow) is more powerful than all of them combined. (Willow whimpers) So I say we change the rule."
Willow didn't create new slayers, she tapped into the well of Slayer power using the scythe as a conduit and changed the one slayer rule - thats all. So it means the spell wasn't a complex as creating new slayers, she just removed the one slayer clause.