Generally pokemon don't like to be set up on. Especially by the #1 used pokemon for the last 2 months with a sky high attack. There's a reason celebi has been using hp fire more recently, to not allow scizor to set up on it. You're assuming that you have every single one of your pokemon at full health. At the very worse hp fire could act as a last ditch move to take down scizor. However, on a pokemon as slow as P2, I don't think it works well enough to warrant a slash, at best it belongs in other options. Discharge hits scizor plenty hard anyways and if you're lucky you'll get a paralysis. I'd like to note that cressy as an "overspecified counter" is not fair to cressy, if you had said something like scarfcune, that would have been better. And lastly, "easily walled by stuff" is extremely vague, and doesn't exactly help your argument. And of course toxic is invaluable on P2, as it allows it to beat, say, zapdos.
