Iron bundle is a pokemon with no switch ins, and to be honest, it isn't more broken cause terastelizing exists. The fact it exists is holding back it's power by a lot and I'll quickly explain why:
This is the team that I've been running the most since day 1. I changed some mons in it once or twice but I found this to be pretty balanced.
https://pokepast.es/dc37870de386cf52
Truth is, many iron bundle sets are running booster energy or specs, because if that wasn't the case, counterplay against it would be impossible. Being an ice type, he takes a bunch of damage from rocks and is weak against most priorities. Steel priorities he can avoid because of his water typing, but fighting still hits hard and there is a good amount in the tier. This being said, it's amazing a pokemon that has no apparent switch ins, and can get a mon per predict hit isn't considered more broken than palafin, but he needs to be banned aswell since he is just something else.
For a long time I ran scarf palafin so I could always threaten with cc, but I later on changed to band so now these would be my team's damage calcs against it.
0 Atk Breloom Mach Punch vs. 0 HP / 0 Def Iron Bundle: 50-62 (38.1 - 47.3%) -- guaranteed 3HKO
252+ Atk Lokix First Impression vs. 0 HP / 0 Def Iron Bundle: 64-76 (48.8 - 58%) -- 95.3% chance to 2HKO
252+ Atk Lokix Sucker Punch vs. 0 HP / 0 Def Iron Bundle: 51-60 (38.9 - 45.8%) -- guaranteed 3HKO
252+ Atk Choice Band Palafin Flip Turn vs. 0 HP / 0 Def Iron Bundle: 44-52 (33.5 - 39.6%) -- guaranteed 3HKO
252 SpA Flutter Mane Moonblast vs. 0 HP / 0 SpD Iron Bundle: 126-148 (96.1 - 112.9%) -- 75% chance to OHKO
252 SpA Flutter Mane Hex (130 BP) vs. 0 HP / 0 SpD Iron Bundle: 171-202 (130.5 - 154.1%) -- guaranteed OHKO
252 SpA Iron Moth Fiery Dance vs. 0 HP / 0 SpD Iron Bundle: 109-129 (83.2 - 98.4%) -- guaranteed 2HKO
As you can see, my best attackers aren't really able to touch him outside of flutter and iron moth, since the others get outsped or killed after using priority, so how can you hold this mon down? What I've been using to deal with such threat is simple, terastelize. I predict switches, go to my iron moth, and tera grass to survive hydro and hit back hard. Yes this is absolute bs but it's the best a person can come up to. If it switches to try to threaten my breloom I can tera electric and throw a close combat. Venoshock and Hex with toxic spikes up guarantee me the KO, so by outspeeding if it isn't holding speed booster item or by simply using a tera grass to survive an hydro pump I guarantee that I won't be seeing that thing no longer. With toxic spikes I can chip it down and to be honest it hates to switch into any of my mons so that is what really helps me a lot. Being real, my team is not the best one at countering him, but when you're trying to hold back a pokemon that has coverage agaisnt the whole tier I don't feel like that's really a point either. I find myself getting him chipped down enough to kill with priority, even having to sacrifice a pokemon at times if he has a moveset and stat spread that can destroy me, being forced to predict certain attacks and waste my terastelize in order to avoid getting sweeped by it. Actually, most of the times I see myself using terastelize in order to save myself, even if to get a priority stronger like first impression or jet punch. My team was made with the intention of stopping any type of attack that included boosting, although it does struggle against things like shed tail dragonite (Which btw I won games purely by starting with orthworm holding a chople, surviving a fighting type move, shed tailing to dragonite and dragon dancing to sweep, it's kinda op) it is quite good at, for example, threatning to kill roaring moon in one hit if it doesn't switch with first impression, and if I waste his tera, better, I've got tinted lens to deal more than 50% and my palafin can ko. (The high amount of priorities is rly strong btw so I rly advise y'all to try)
I'm getting a little bit off the trail here, but what I mean is, even a team made to handle most threats in the tier has to literally predict attacks in order to switch into something that can survive the attacks of that metallic bird.
Btw right now moves like curse/bulk up are getting really good, so I advise you all to try it, good mons for that are things like great tusk, dondozo, (Palafin but he is prob getting banned next), anhinihilape, and you even have iron defense users like garganacl.