I don't know how to make this clearer. If there are four commonly used fairy type special attacking pokemon in OU, DO NOT USE A 4X WEAK TO FAIRY POKEMON AS A GENERIC SPECIAL WALL.
By this logic, you shouldn't use AV Crown either since it loses to commo special attackers like Darkrai, Iron Moth, Wake, Pult, and Valiant if it has the right coverage like Knock Off or Shadow Ball. Why have Volt switch when it is entirely countered by Ground types? Well, the answer is that it has enough utility into enough things to be worth it. Furthermore, I would also like to correct you that this is more of a bulky pivot than a pure wall, which functions somewhat differently.
I understand what you are saying about the 4X weakness and Fairy coverage moves are common. Checking Darkrai is pretty good. You don't think the benefits outweigh the negatives. But outright ignoring the benefits won't make a convincing argument to me.
I remember discussing Tapu Koko's set diversity with you a while back. I can admire wanting to push a mon's potential, but you have a tendency to overestimate the extent to which mons can effectively run different sets in general.
Roaring Moon lacks any progress making capability outside of a weak knock off and u turn, which is cool, but too slow at making progress. Also a massive coverage issue since it basically can't touch anything that beats it - ur gonna be letting a lot of things in for free. Spdef Moon doesn't even beat standard Raging Bolt 1v1 btw.
Boots spdef is gonna be forced to Roost quite often as well, so you're gonna be giving up free turns. This lack of passive recovery is probably the biggest issue (AV Moon is very good in AAA for what it's worth).
And the AV set is just straight up not good. You cannot even touch some of the most relevant and threatening mons in the tier, and u get obliterated by hazards and have 0 longevity. Just use Ting Lu.
The typing is pretty bad defensively, the reason why Carl The Turtle is listing those pokemon is because they are some of the most relevant special attackers in the tier. Ting Lu gets away with it because of the ground typing which lets it beat twave/electrics and block volt switch. Ting Lu is also significantly better at making progress with Spikes/Ruination/Whirlwind, and has much higher defensive stats. Ting Lu also isn't meant to be a long term check anyway (and this is fine since it can reliably get up 3 layers in most games), unlike your Moon set.
Anyway, people have been experimenting with Roaring Moon. Scarf moon popped up a few months back, and you see some non-flying teras on booster dd acro in recent tournaments. It's this kind of experimentation that is most effective, not trying to make a Pokemon do something it was never meant to do and that other mons can do much better.
Iirc, you were citing Roaring Moon's potential set diversity as a reason for why you think it's broken. I urge you to reconsider the merit and more importantly the flaws of the sets you are experimenting with and you will probably come to a different conclusion. Would not mind if you included some replays as well.
This is a lot to address. The Tapu Koko debate was a hypothetical that cannot be tested. And Nat Dex has a lot of factors like Z moves, Megas, and Ferrothorn that don't translate to an OU metagame. I know a little bit more than the average Joe on game design. So I understand mechanics and how Quark Drive might interact in an OU metagame. While this doesn't mean I'm always right, I generally understand the mechanics beyond what might be considered conventional metagame wisdom.
As for AV Roaring Moon, this is a bit of a misrepresentation of my actual stance. I made it clear in my initial comment and several after that it needs more testing. And so far, I only tested AV on low ladder. I was hoping for maybe more brainstorming rather than certain regressive things. But undeniably, there are certain benefits to AV Moon. Whether the benefits outweigh the negatives is a different matter. What I mainly take issue with is certain arguments.
The lack of progress and free switch in points were already addressed, though. It's not a good argument in this case, especially the free switch. You take a hit as the bulky pivot you are, and then you U-turn into your counterplay, Dragon Tail the setup mon or the predicted free switch so they take more hazard chip, or destroy an item. It isn't free. And if you have any other defensive backbone on your team, you can probably steal back momentum with the right mons anyways.
Boots was a suggestion by another poster because of Roost, but I haven't tested it. It's pure theorymon at this point. It might not be good. I'm just open minded about it. There was a couple breaking swipe sets awhile back that someone posted that seemed to work ok.
The AV Moon set was tested so far with Wish support on low ladder. There was an AV Scizor concept while Kyurem was a thing. Now that Kyurem is banned, Moon has a better shot to be relevant defensively. Ting Lu is good and probably better. But it's slow and not a pivot. It also isn't taking Water or Grass moves as well without Tera. It isn't the same kind of set.
Seeing Moon set diversity experimentation is good, but it's far from what the potential of the mon is. I had several posters just now talk about how you should just use booster Acro or to only use it as a breaker/sweeper. This suggests some people think the opposite about experimentation with Roaring Moon. As for what Moon was "meant" to do, it has HP and Sp. Attack both higher than base 100 with many good resistances. I feel like it's too soon to outright dismiss it like this.
Finally, the reason I think Moon is broken isn't what you stated. First of all, DD + BE + Tera is inherently problematic from a game design perspective. The set diversity part is about changing counterplay, which primarily centers around DD sets changing coverage and counterplay somewhat similarly to Gouging Fire. If the AV Moon set is viable, it would certainly never be broken. It would just be another thing the mon could do. Kinda like the Sap Sipper trapping Azu sets from several gens back.
I do have a few questionable low ladder replays, but I don't entirely know the value of them at this point. I will show a few since you asked.
Here, I let Sun Venusaur gets to plus 3. AV Moon lives the hit and almost phases it out, but the Dragon Tail misses:
https://replay.pokemonshowdown.com/gen9ou-2218927971
Goofy game against goofy mono Ice team, but Moon was able to counter Glowking and a Quiver Dance mon pretty freely:
https://replay.pokemonshowdown.com/gen9ou-2218935656
Probably the best of these not great replays. AV Moon helped bully Iron Crown and Great Tusk. You can at least see the pivoting flow despite the other misplays. This is how the set is supposed to function:
https://replay.pokemonshowdown.com/gen9ou-2218938752
Personally, I'd say these are mostly low quality replays for various reasons. The team I threw together was hardly a team. I was't planning to show any replays until I got some better quality stuff at later stages of testing. But it is what it is. I hope people don't take the wrong things away from this. Bad replays on low ladder were never meant to be proof of viability. That's obviously
not the point of me showing these.
, 
, 
, and even somewhat 
can come in for free? it takes big damage from a common 
and 
coverage move, can't really eat hits from specs 
and 
that well, and cannot switch into and is susceptible to being counter-tera'd by 
? Even by non-OU mons that see usage, 
isn't a safe switch and 
always runs a super effective move? 
doesn't even target it's spdef stat with the super effective move?
see use, because they ANSWER the pokemon listed above to a very strong degree through super effective STAB/coverage pressure or through ticking status or permanently making the mon move at half speed through a coinflip while also exerting pressure into whatever switches in.
