Your Toxicroak that takes 71.4% - 84.4% from Head Smash checks Aggron?
The same way your Rhyperior is somehow better then their Rhyperior who gets a one turn advantage and all it needs to do is 67.9% - 80.4% to flat out beat you anyway (ie if you switch into Stone Edge, you lose). That has absolutely nothing to do with prediction, don't try to claim that as my argument when my argument is clearly "those checks are shitty and won't work in almost every scenario". It's not a matter of prediction when you can predict correctly and still get destroyed.
First of all, I've already covered this. If I think Rhyperior is going to attack instead of set up, I'll switch to Toxicroak, Torterra, or Mespirit, not my own Rhyperior.
If it does set up or makes the wrong move, then I made a wrong prediction and I will be losing a Pokemon. That's how this game works.
Honestly it's like saying "Latias can't check DDMence because it could just outrage right away". Well yes, but no Mence ever Outrages right away, because that's stupid, so people still consider Latias a check to DDMence. And if you switch in a Latias into Draco Meteor you can't exactly complain about it being a "shitty check"; you just don't know how to use it.
Oh and yeah, my Toxicroak checks Aggron without Earthquake because it either a) Rock Polishes, meaning I come in at nearly full health and survive the head smash or B) attacks, meaning I'm faster and can attack for the KO or force it out. That's what "checking" means, please familiarize yourself with the term before continuing the discussion.
There comes a point when sweeping with Swellow is a valid option, and your opponent may still have something like RP Aggron/Rhyperior left. There is also the possibility that you are revenge killing something, which is one of Swellow's biggest perks as a sweeper: it's faster then everything.
In that case you need to put up with the fact that revenge killing with such an easily walled Pokemon is going to open you up to a ton of threats.
Swellow is one of the best offensive sweepers if not the best. It is a great asset vs both stall and offense because of U-turn, status immunity, and Speed.
No competent stall team is ever going to let you U-Turn all over the place, and neither is it beneficial for you to do so with Hazards and Toxic Orb eating a third of its health every time it comes in. Not to mention that nothing on stall will ever die immediately to Facade, so there's really no reason to switch out; hell, things like Milotic can stall it out easily, and even Chansey survives a hit if it's Bold!. Only if you bring in Swellow on something like Venusaur (good luck eating a sludge bomb, no good user will powder if they know you have a Toxic'd swellow) will you ever get to successfully U-Turn.
I will grant that Swellow outruns pretty much everything on offense, so if you ever run into an offensive team consisting of Blazikens and Venusaurs you'll probably sweep it. However, against other offensive teams (i.e. well built ones), you'll continuously run into Pokemon like Rotom, Rhyperior, Aggron, Mespirit, Spiritomb, Donphan, etc. etc. who can easily tank a +1 Facade or Brave Bird and massacre you. You could U-Turn out of these, sure, but you just lost 32% of your health.
Sweepers in UU that rely on STAB that gets mostly neutral coverage will never be good in my eyes. UU Sweepers need good SE coverage against a large number of Pokemon to really be efficient, mostly because we don't have something with base 100+ offenses that can spam Draco Meteor down here, so defense in UU is more dependent on typing than straight out stats. I could go on about this but this isn't really the place. Suffice to say that I don't consider Swellow much of a threat at all.
Scarf Primape has this neat move called U-turn where your opponent switches their counter in and takes Spikes/SR/U-turn damage and lets you switch out in one turn. So if Spiritomb comes in, I'm going to U-turn to Moltres. Once Moltres is in, you know what's coming in at least soon: Chansey. Spiritomb can't keep taking U-turns and Spikes damage, Primape is eventually going to just break through it. Similar thing happens with Venusaur, Milotic, etc.
This is even worse than your Swellow example. What would possibly switch out of Primeape on stall? Chansey? It's just going to Protect to scout your move and then stay in if it's U-Turn. Venusaur? Why? Even specially defensive variants aren't 2hko'd by Ice Punch (45.6% - 53.8%, physically defensive ones take way, way less), and it'll just smack you around with sludge bomb and outstall with Synthesis. Milotic? Lol, 36.1% - 42.7% from Close Combat. Registeel? Maybe. Or it could just stay in, easily survive the Close Combat (61% - 72.5%) and paralyze your goofy ass. It's even worse if you U-Turn since then it's Moltres getting paralyzed. Seriously, what kind of stall teams are you facing that are letting your non-threatening sweepers U-Turn all over the place?
You were accusing me of being "unfair" with prediction earlier and now Chansey - a teams crutch special wall - is going to stay in on Absol - one of the most dangerous sweepers a stall team can face? No, it won't.
Uh, yes it will, unless you subscribe to the "DD Lapras" school of prediction thought. A player who knows your Absol is scarfed has absolutely no reason to switch out once he Protects and finds out you didn't use Superpower. Surprise value is not a legitimate argument for the utility of a Pokemon, if it were I could say that Hitmonlee beats Tangrowth by getting three hits against it because my opponent doesn't know it has Limber and uses Stun Spore
And you don't just switch Absol into Ghosts, you hit it with Stone Edge or Assurance with Donphan once, and then switch it in next time. Absol can stop the ghosts from fleeing and recovering on something like Swellow.
Oh okay so now you need excellent prediction on your side and your opponent being completely brain dead and not using WoW on the switch for a scarfer who is supposedly "great against stall" to beat defensively frail Pokemon that are weak to its STAB. You've won me over, Absol is clearly the UU incaration of NP Mixape.
It depends where you're drawing the line of this "hyper offense" team. There isn't much a team with a bunch of fast heavy hitters can do to stop threats besides hit harder and faster then them. A Scarfer is one of the options to deal with them, priority is the other
Does offense in general really need those? No, not as much as a "hyper offense" team would need.
A team with a bunch of frail stat-uppers obviously won't be able to handle other threats once they set up. That's why these sorts of teams rely on "not letting them set up". A scarfer directly contradicts this idea by locking itself into an unboosted move. You might say a hyper offense team would need a scarf rotom to revenge a DD Feraligatr once it sets up, but what happens when your opponent immediately switches in an RPerior? How can a defensively frail offensive team handle that?
This is why scarfers are discouraged on Hyper Offense; I call it "Dugtrio syndrome". Scarfers might be able to revenge dangerous threats, but they do so at the cost of letting OTHER dangerous threats have easy set up, which prevents them from being very useful on such a team.