You have some very nice formatting. I do though have some differing views.I want to talk about the absolute state of entry hazard control in this metagame, and what that means for teambuilding.
Here is a screenshot of every fully evolved Defogger currently in SV:
View attachment 469651
Outside of Corviknight, that list is dire. Noivern is obviously a good mon, but does not have the bulk to be a passable Defogger. Scizor would have been passible last gen, but the loss of Roost and Knock Off is devastating for it, and Talonflame's famed MGLO sets do not keep up with the higher power level (or dumb new Speed tiers) in SV. In short, outside of Corviknight, we arguably have zero other viable Defoggers.
Here is the same screenshot for spinners:
View attachment 469652
On the Rapid Spin front we are doing a little better; Great Tusk and Iron Treads are great mons, but lack native recovery so have to compete for coveted Regenerator and Poison Heal slots. Cyclizar has amazing utility in general, but is likely limited to more offensive teams and again, competes for a Regen slot. Avalugg either desperately wants to take the Tera slot or is hindered by an awful typing, while Quaquaval seems fine on offensive teams ig? But still, very little sustainability. Everything past that is fairy niche.
Other Removal (Mortal Spin and Tidy Up)
Tidy Up is a hilariously broken move, but only on Maushold, which certainly does not have the bulk or recovery to be a reliable hazard remover. Mortal Spin is similarly relegated to Glimmora which has a...suspect...typing and no native recovery. Neither of these should be considered consistent removal options.
Entry Hazard Prevention (Magic Bounce)
Magic Bounce is the other semi-reliable way to control hazards, but has two key drawbacks. First, it needs to be able to actively switch into the entry hazard setters, and if you are aware of a Magic Bounce user that can come in on every Rocks/Spikes/Toxic Spikes user, please let me know. Secondly, it requires giving up the ability slot, which in the FurScales meta, is a big ask. This is also unreliable into Moldy users, which are much more relevant this generation thanks to bypassing FurScales as well.
What does this all mean?
Realistically, most teams will be relying on one of Corviknight, Great Tusk, or Iron Treads for hazard removal. This creates a problem, as all of them can be blanked by either Good as Gold or Ghost-types, making hazard stack a potent option. The decline of Magic Guard and Regenerator, plus the more limited PP of recovery moves, all amplify the effect of entry hazards. Heavy-Duty Boots has a higher cost as well, as it means you have to forgo the passive recovery of Leftovers for walls and are more likely to struggle against Poison Heal, Fur Coat, and Ice Scales as an attacker.
Skeledirge @ Heavy-Duty Boots
Ability: Good as Gold
EVs: 248 HP / 252 Def / 8 SpD
IVs: 0 Atk
- Torch Song
- Slack Off
Meet Corviknight's worst nightmare. Good as Gold blocks any Defog attempts, Wisp punishes incoming attackers, and Torch Song can snowball against more passive teams. Wisp can also potentially beat non-Poison Heal variants of Iron Threads and Great Tusks. Slack Off provides excellent longevity, allowing it generally outlast Corviknight and common spinners.
Palossand @ Heavy-Duty Boots / Leftovers
Ability: Good as Gold
EVs: 248 HP / 252 Def / 8 SpD
IVs: 0 Atk
- Shore Up
- Shadow Ball / Earth Power
- Stealth Rock / Earth Power
- Skill Swap
A more passive but more dedicated spinblocker. It has more favorable matchup into Iron Threads and can punish Poison Heal Great Tusk with Skill Swap, but is much more passive, especially against Corv. If you want hazards up though, it is a great removal denial option.
Is this a problem?
Short answer, remains to be seen. Magic Bounce will always make hazard stacking risky, and Poison Heal mons are able to sit on hazard stackers all day long; however, both abilities have been banned before and might be again. FurScales is also high on the watch list, and if it is removed, perhaps hazard stackers will even more easily overpower opposing walls. Or, maybe we will just all cope and run Mold Breaker Defog. It's way too early to tell, but I definitely have my eye on how overpowering hazard stacking can be; it's certainly not at the top of the watchlist, but I am very curious to see how the hazard metagame revolves.
Talon Flame and Noivern and Hawlucha are actually great defoggers. A reason Noivern can get annoying is because aside from hitting hard, it can actually afford to run roost and when it gets it, it can only really be forced out by something it cannot damage like a blissey. Bulkier setters cannot really pack enough of a punch to threaten it.
Stone edge is a rare sight on treads and tusk due to them running rapid spin. Even then, without counting abilities, Great tusk who is probably the most offensive of the setters with maximum attack EVs and nature is just barely ohkoing a 2x weak Noivern with 0 EVs in HP and Defense using stone edge 62% chance 80% to 110% damage. Being a Flying type that has some form of recovery in general makes some a viable defogger and it's the hazard setter who has to account for that.
Rapid Spinners in general lack natural recovery as the move has one of the highest pp. I don't really see competing for ability slots as a substantial argument for this case, especially when considering nearly all of the abilities are available this gen. Competition for ability slots is part of aaa's nature in general, majority of rapid Spinners can make good use Regen since Regen is normally run as a means of recovery for mons with no natural recovery. Both corv and Avalugg compete for well baked but both make good use of it either was. Same with -ate abilities for offensive mons. 50% of the rapid Spinners are also hazard setters themselves. Cyclizar is great utility because it has Regen. Majority of ghost types would also be heavily damaged by the rapid spinner going for any other move they aren't immune to, the plan being to little the rapid spinner down so they don't have to worry about it anymore, something regenerator would mitigate quite well. Alot of ghost types also do not get knock off while rapid Spinners do.
Avalugg ... does not desperately want the terra slot. It is ice type to nerf it due to its incredible defensive stats that allows it to tank even super effective moves with comfort. Despite its typing, it is typically one of the last mons to fall as well as one of the most frequently switched in. Ting-lu, aggron, and such monsters with high defensive capabilities are given their typings because they can tank things so well.
In this OM maushold can indeed be made into a reliable hazard remover. Tidy Up is indeed an op move in that its hazard removal capabilities can only be negated by taunt.
Glimmora ... does indeed have a suspect type.
... Every ability requires you to sacrifice an ability slot and magic bounce is not a bad ability. It's actually in the same tier as good as gold. What's beging overlooked hazard setters aren't running mold breaking abilities right now. The presence of magic bounce is what usually forces that. With this being a new gen people are still experimenting. Slither wing is actually an excellent magic bouncer that is able to switch in and even set up on majority of hazard setters, even coming with its own natural recovery. Bug/Fighting is an excellent combo considering majority of hazard setters are walled by it and take either neutral or super effective damage from it. The same "takes up an ability slots" argument serves as a double edged sword. If they run mold breaker on their hazard setters, they take it away from a Mon that could use it to bypass a type immunity ability or damage reduction ability. It also means they need to dedicate a second ability slot to good as gold if they wanted to stop defoggers and is not accounting for the opponents team. You'd be dedicating two pokemon to keep hazards up. Saying magic bounce "takes up and ability slots" sounds like downplaying it and makes it sound like a c tier ability despite being a great ability that gets distributed to sub par mons on purpose due to its power of "no u".
What does it all mean?
Corviknight, Great Tusk, and Treads aren't blanketed by good as gold or ghost types. Those mons are switched in as a prediction that you are going to choose to attempt to remove hazards on a given turn rather than click any other move that'll likely nuke the incoming mon's hp. Corviknight in particular tends to force both good as gold and ghost types out alike. Good as good as also likely to be placed on a ghost type as well, meaning once again corviknight or the other two would kill it or force it out.
There does seem to be a contradiction as well near the end of this section. You say it stat that it helps take down walls but then immediately 180 in the same sentence and say it makes it harder to take down walls. Heavy duty boots always meant forgoing something else, it's why boots are mandatory on virtually every blissey. And they are definitely not a bad item, heck teams with full heavy duty boots are quite difficult to take down or feasible to make survive and serve other purposes than making walls ignore hazards. Cinderace with boots got sent to Ubers as it could keep coming in and eventually get a bulk up off.
Both ghost types you showed are definitely not Corviknight's worst nightmare. The Skeledirge actually gets 100% walled and forced out by Corv. Please do not forget brave bird corv is just as common as body press Corv.
If palosand ever used skill swap ... the hazards can then be defogged. It's also relying on tusk having poison heal and itself being capable of tanking hits from the rapid spinner who may also be a hazard setters their self.
Most of the issues here seem to be more team building oriented rather than hazard related.
I forgot how to use spoiler tags (animated and shiny sprites too). Will shorten this when I figure out how.