Something being able to come in on the hazard setters and other pokemon and get off defogs, does indeed make them a reliable defogger. I didn't mention any sets for them, refresh my memory if I did. I prefer not to spoon feed, providing the slither wing option is already overstepping my generosity in that department as people tend to be too lazy to explore other options. What are you talking about, talonflame is indeed a notorious magic guard user as it uses it to fire off recoilless moves and come in on hazards. If you call removing hazards, halving attacks, or getting KO's and having longevity useless ... I do not really know what to tell you. Brave Bird and Flare Blitz are 120 Power moves, they are indeed doing damage when used by a pokemon with no EVs. You are attempting to downplay something you admittedly do not use. "it can technically run willow-wisp" ... the word technically does not need to be there. People are not using many old mons because once again this is a new gen and everyone is experimenting. You keep using the word useless but I do not think it means what you think it means. Magic Bounce does not get rid of already set hazards and one pokemon cannot check everything.Just because something can Defog to a decent degree I don't think by any means make them reliable Defoggers either. Both the Talonflame and Hawlucha sets you mention would be pretty useless outside of defogging which isn't great. Talonflame isn't a notorious user of MG in this meta since well no one uses Talonflame in this meta. It can technically run Wisp and U-turn for some utility but there are many better mons and it can't hit anything for good damage excluding frail mons that could most likely outspeed and kill in return. Hawlucha is just completely useless, there is no reason to run Hawlucha except to be a dedicated Defog bot and having a mon that can only Defog, well at that point just run a dedicated MBounce mon. Noivern also, what other item or set can afford to run Defog? If you're running Noivern as a pure Defog bot then I'm sorry to say but you've crippled how useful Noivern can actually be as it can now never break any special wall and again otherwise running a pure Defog bot just to get rid of hazards isn't great for a team. Listed examples also really lack bulk themselves to be great defoggers over the game, except Noivern which is a bit sus and again being a really dedicated Defogger with bulk investment and Defog isn't great.
Knock isn't too common true, but it's still there and Tusk is a great mon that can spam Knock well. Also I wouldn't say the prime Good as Gold abusers which I've really only noticed to be Skeleridge is frail at all. 104/100/75 bulk is fine and can be nice physically if invested into, which it usually is and Palossand also isn't frail at all, which I've seen. I've been building balance a lot recently and really... if you want a mon that actually that has use and can actually defog well, then yeah, Corviknight is really your only option. I've played only a few matches against GaG spam but yeah it is super annoying to play against, whether it's super problematic? Idk, there are definitely a lot of things that need to be suspected, im not too sure if it is suspect worthy at all but right there are probably more pressing matters.
You do not seem to comprehend that pokemon can be used for various reasons and purposes and are not just limited to what you Google or see on YouTube videos. You say they lack bulk, yet I do not any world where a hazard setting tusk, treads, tien-lu, gastrodon kills Hawlucha. You say the term defog bot yet Corviknight in his essence is a defog bot, you switch it in on hazards setters to try and stall out their hazards, on things that aren't obvious nukes, and on certain choice locked moves you expect to happen. Skeledirge isn't a prime good as gold abuser, the set farther above was just made as an example and they thought it walled corviknight, and someone had to advise them to use lick of all moves. Its bulk is nothing to something that would come in and kill it, it's not a perfect pokemon those being. Riiiight, palosand why by your same logic doesn't exist.
Knock is there ... on primarily the hazard setters, the things you switch the birds in on. Corviknight isn't the only option, it's the most common option used, one that everyone expects.
On the subject of breaking special walls ... with a special attacker. 90% of the time you won't break that special wall with a stab psyshock because ... that is the purpose of a special wall. Even if you were to trick one that doesn't mean it cannot still wall you, until it is dead you have only really slowed it down. Last gen it seems that no one realized that bullet proof stunfish was nigh unbreakable and one of the best special walls possible.