I'd argue that Normal is probably the second best stab to attack with after Dragon and Water. It is really only resisted by Rock, Steel, and an immunity by Ghost.
Draco Meteor technically does have a downside of -2 SAtk but the users are often so strong that it still does have damage and boosted Draco Meteors will often 1-2 hit ko most thing, even things that resist that unless they'tre super bulky. And yes, a strong special attack will put Slaking out (Darkrai, Gengar, Latios, Heatran, and Shaymin-S if it starts flinch haxing you and I'm not sure if Mummy would work on Air Slash). It needs a bit more support than most Pokemon. That is why Team Viewer is such a gift to see if they have something that threatens Slaking so it is known if they have Latios, Hippowdon, Skarmory, Darkrai, etc. While this is a fun strategy, I doubt that most people would see it coming since few would likely use it. But once certain threats are gone, it could viably work.
Um...Regigigas doesn't learn Bulk Up and never has. It does now learn a Protect clone Wide Guard (that protects all team mate partners which would make it really good in double/triples) since it never learned the Original Protect. Regigias also does not have the same physical bulk as Slaking or a recovery move and it's ability is arguably worse for an attacker than Truant (unless facing Sub/Protect). I like Regigigas but it is horrible in singles unless you're running a Status set with Thunderwave/Toxic/Confuse Ray and the like with some coverage moves and try stalling down time (which now that it does have a Protect becomes MUCH easier and it will have to be tried out again but Phazers suck if they're still alive).
Roopushin's Drain Punch is strong but not as good as a Slack Off and is less physically defensive in comparison to Slaking. Actually, Slaking has better Special Defensive capabilities due to higher hp since Slaking and Roopushin have the same sucky special defense base stat. Normal has less weaknesses (only to fighting) while Roopushin has to deal with Psychic and Flying (Shaymin-S and Psychic types like Rankurusu). Slaking is also technically faster and does not need to rely on Mach Punch to hit faster foes and if this strategy works, Slaking is much better than Roopushin because of the better stab power, bulk, and Slack Off. I love Roopushin. But in this case, Slaking is better and if Slaking never had Truant, it would have been Uber because of 100 base speed (outspeed the common uber mark), has ridiculous surviveability and bulk with Bulk Up and Slack Off, 160 base attack, etc. Plus Slaking has SUCKER PUNCH (assuming without Truant) in Ubers which smacks things, punches, useable special attack, etc. Truant was their way of giving it balance, if only just a little too much, especially for OU.
Roopushin loses against Slaking with Bulk Up and Mach Punch doesn't 2 hit ko. Actually after Bulk Up, Roopushin's Drain Punch wouldn't 2 hit ko either without a boost of it's own while an unboosted Frustration 2 hit koes most Roopushins unless they Bulk Up but with Spikes it would still die to Frustration. Roopushin can't take Air Slashes or Psychics either so a strong one does massive damage to it as well
You're slightly wrong about the power increase making things like Slaking (if this is successfully pulled off) no longer a "big deal". They hit hard. But few things have the Bulk of Slaking which once Truant is gone will DESTROY teams without a powerful special attacker or phazer or Terakion left. An unboosted Frustration 2 hit koes Doryuzu with Stealth Rock, despite the resist and 4x rock resist but once Doryuzu has Swords Dance. Slaking can take a +2 Earthquake and beat the crap out of Balloon Doryuzu which says something. Doryuzu needs Life Orb to beat Slaking and since most don't, Slaking can 2 hit ko with a resisted move. After Bulk Up, Slaking can survive Life Orb Blaziken Hi Jump Kick and pretty much everything that is physically weaker. After Bulk Up, Slaking ohkoes Garchomp while even before Bulk Up, Choice Scarf Outrage couldn't 2 hit ko and after Bulk Up it becomes set up bait.
Again, if and only if, the Mummy strategy is pulled off, Slaking is far superior to pretty much every Pokemon and the only physical thing that is koing is going to be Terakion with stab Close Combat and being able to easily survive +1 Frustration with only slightly less than half health because of resist while Slaking needs Bulk Up to avoid being ohkoed by Close Combat while Terakion is faster. Lucario if there isn't triple layer of spikes will also beat it but Slaking wins with Spikes and a Bulk Up before Lucario came in. But otherwise, nothing physical koes.
Oh, and, Slaking survives a max SAtk Blaziken Life Orb Fireblast which deals 72.11% damage. The special attacks that ko Slaking have to be either super effective from base 130+ base SAtk and Life Orb or mega powerful stab with 130+ base SAtk. It is ridiculous. And it isn't inconceviable that this strategy can work once phazers are gone. With Team support, Slaking will rip people apart.
