Not Trick+Sticky Barb btw, Hatt will eat Gliscor's Knock Off and then use contact moves like Draining Kiss/Nuzzle as Clefable switches in, that is enough to pass the Sticky Barb. Clefable does not need to spend a turn or commit a moveslot to Trick, just to be clear. Extremely easy to cripple Hatt in this case.
As stated multiple times, these steel types are getting chipped by spikes, knock, etc and are losing long term vs a well built gliscor team.
When I said defog roost ID on corv, I did not mean all of those moves on the same set, because that is quite unviable just to be clear. Defog/roost/ID on Corv means you must either drop Body Press or U-turn, and dropping either is usually a horrible idea. So off the bat this situation is quite unrealistic.
I think you're jumbling up numbers here. When you state Gliscor having 16 Protects, 16 Spikes, 16 Knocks, and 8 Toxics, you are taking Pressure into account, but when you say Iron Defense works just fine, how are you hitting 48 pp? ID only has 24 pp, you are theoretically taking away 48 Gliscor pp but since you've already taken Pressure into account while listing numbers, you're just confusing us now.
Of course, this situation is not going to happen very much to begin with, because Gliscor does not need to stay in and waste all its pp. If you are going to sit there and click ID/Defog, Clefable and Gliscor can switch back and forth and just wait it out. You state that "it needs to switch out, which you can as well, no big deal" BUT THIS IS WRONG! Clefable and Gliscor can switch back and forth while taking ZERO net damage from hazards, but Corv+whatever is taking at least 12.5% Rocks damage by switching back and forth. Once again, this is a losing position for you.
Corv's attacks are sealed up due to Clefable's Sticky Barb, Corv's item gets Knocked, and it cannot infinitely switch under max layers without an item the same way Gliscor+Clefable can. Not to mention, if you mispredict and switch out Corv as Gliscor clicks Knock Off, that is more progress made by the Gliscor team.
The subtle implication here is the acceptance that all slow teams need Gliscor now. This is exactly we should ban this mon, because it's either offense or Gliscor fat if you want to succeed consistently now.
Tusk+Ace used to be able to support balance and BO, the fact that these teams must now be fast paced enough to let Great Tusk get Toxic'd is horrifically limiting, whether you realize it or not.
This automatic assumption of Gliscor protecting each other turn can also be taken advantage of, you do still need to predict. Gliscor players are not just mindless robots who spam protect lol.
Gliscor teams can take those magma storms, taunts, and NP gholdengos, that's the way they're built, so that you beat those balloon steel types long term with hazards, not fold to them immediately.
Why is it surprising to use Tera on your wallbreaker when fighting fat? Is it also shocking to tera dragon ur cb bax?? Or tera water ur specs proto SpA WW under sun? You use hammy with pivots like U-turn Zapdos which force in mons like Clodsire, you get your free turns and click Knock Off, get Spikes up, and then Tera Water to Aqua Cutter through whatever is tanking your knocks. There are many lines for progress and idk where the confusion is.
So...is Gliscor a threat to offense or not? In one paragraph you are telling me the mon with 90/80/65 bulk, 85 speed, and 5 weaknesses is a threat to offense teams more than Gliscor (I disagree), and in the next paragraph you are telling me offensive teams matchup well vs Gliscor??
Even if you only toxic a key threat and get up a spike vs offense, Gliscor has often done its job and can leave the heavy duty walling to its more passive teammates. They can make progress they otherwise couldn't have because of what Gliscor did.
So after hatt eats a barb, my gliscor gets to protect and gain 12.5% health as your hatterene comes in and loses 12.5% health. This is somehow a bad thing and I'm not freely forcing progress? I really fail to see how.