If you're using flygon to sweep, you're not capitalizing on it's greatest attributes; Scouting and cleaning. The fact that it can 2ko porygon2 w/o getting locked into a move is excellent. I'm pretty sure you've all been at that position were you've desperately wanted to click outrage to finish off a wall but knew a bulky steal or weavile was waiting in the midst to revenge kill you. With superpower you can get the vital KO's on things like snorlax w/o being setup bait as you normally would if you used outrage/earthquake. Steal types and fast scarfers are everywhere. If you use outrage chances are you'll either be walled or revenge killed. If you use earthquake there are an abundance of pokemon who have an immunity to that move and can use flygon to set up. There are no more than about 5-6 viable ghost types in uu as opposed to the numerous earthquake immunity pokes. If anything superpower helps it clean more effectively.
I completely agree with the first part of your post. Flygon is an amazing scouter and cleaner, and although it is by no means the only viable set, there is a reason that Scarf is most common. However, a -1 or -2 non STAB Superpower is about as easy to set up on as an Earthquake immunity. Lets say you catch Snorlax/Umberon on the switch and 2HKO them (the
offensive variant of P2 is never 2HKO'd by Scarf Superpower).
-3 Superpower (Intimidate) vs 4/0 Arcanine: 16.5% - 19.6%
-2 Superpower vs 4/0 Azelf: 12.3% - 14.7%
-2 Superpower vs 252/0 Azumarill: 16.3% - 19.3%
-2 Superpower vs 252/252 + Blastoise: 10.8% - 13%
-2 Superpower vs 252/80 Bronzong: 13.3% - 16%
-2 Superpower vs 252/114 + Claydol: 6.5% - 7.7%
-2 Superpower vs 4/0 Cobalion: 24.7% - 29.6%
-2 Superpower vs 4/0 Crobat: 4.8% - 5.4%
-2 Superpower vs 4/0 Darmanitan: 22.7% - 27%
-2 Superpower vs 252/4 Empoleon: 30.1% - 35.5%
-2 Superpower vs 252/0 Bisharp: 59.9% - 70.7%
-1 Superpower vs 252/0 Bisharp: 80.2% - 94.6%
I was going to continue, but I think I made my point. This is a -2 Superpower against frail Pokemon, against defensive Pokemon, against both defensive and frail steels. Bisharp has only 65/100 defensives, is x4 weak, and Flygon can't even reliably OHKO at -1. So even if you do manage to 2HKO Snorlax and Umbreon, which isn't even a sure thing, you become set up bait for literally the entire tier. And thats all assuming Snorlax or Umbreon switched into Flygon, to at least give him the momentum (there are many better switches). If Flygon comes in on Snorlax, hoping to scare him:
Scarfgon Superpower (-0) vs 208/124 Snorlax: 50.7% - 60%
0 attack Snorlax Body Slam vs -1 4/0 Flygon: 59.8% - 70.8%
The Flygon comes out on top, but barely. Assuming he isn't paralyzed, he is at low health, at -2, and probably as good as dead.
Senario against Umbreon:
Umbreon comes in on SR: 88% health.
Flygon superpowrs for a max of 60%, Umberon is at 28%.
Lefties brings to 34%
Umberon protects, 40%
Superpower only hits 40% at max damage
again, which isn't likely, so Umbreon is at low health and Wishes. Protects and is at about 60% again.
It's cool, sure. But I don't think very useful.
Edit: On a completely different note
Will Regen Alomomola get any love? I used it a few times on wifi and stuff and it's a very reliable wish passer. Slowbro kind of outclasses it as a straight up wall due to having an offensive presence. But Slowbro can't wish pass a million times a match. ;)
Just saw this. Hmmm after a few calcs it seems like Alomomola is bulkier on both sides. Loss of offensive presence is rough, but Wish Passing 267 HP is amazing. Soak can potentially ruin an attacker's STAB, which could really change damage output, and it opens defensive mons up to Toxic if they are immune. Regenerator means it doesn't even have to Wish + Protect, it can just Wish and switch. It looks like a really killer supporter to me.