An-94 my man, I feel like you are, like most people who are newer to the forums and suspect debates on them, slightly misguided about a few things. For one, simply replying to every person in the thread in multiple posts doesn't make your point seem viable, it makes it seem like you are on the defensive without a singular solid argument (which you are) and wanting attention more than a certain tiering decision. That's mostly my opinion though, so take it or leave it. I also giggled at the statement that we should "leave yanma its mangable if u cant deal with it ur bad" [sic]. Whether or not something is broken has absolutely nothing to do with player skill level. In fact, a broken Pokemon makes it more difficult to actually deduce player skill level from the ladder as people using the broken Pokemon (not necessarily the most skilled players) will succeed while others will not succeed as much. In this post, I'm going to argue for why Yanma is indeed broken and expand on the suspect system we are using this gen, because although I think it's a different topic, I do believe it's one worth defending to people that are newer to the system if only for clarification.
Yanma is assuredly overpowered in the LC metagame. At its base, that word just means it "defeats or overcomes opponents with superior strength", and while that is not necessarily the typical definition used for competitive purposes, it actually applies to Yanma quite well. Here are some objective things, just looking at Yanma's stats / typing, that could cause you to deduce this.
20 Speed: 20 Speed is not inherently broken, it's what the Pokemon can do with it. First, let's just compare Yanma to the other 20 Speed Pokemon: Diglett- since it cannot run an Adamant nature if it wants to hit 20 Speed, Diglett hits a maximum Attack stat of 15 with a base stat of 45. This sounds fine by LC standards, but compare it to Yanma: Yanmaactually has a higher base Atk than Diglett at 65, and
that's not even to mention the fact that it's Special Attack reaches 14, just one point lower than Diglett's max offensive prowess, without any investment. In fact, no Pokemon in the 20 Speed tier has any offensive stat that is greater than 65 (Elekid ties it), which is Yanma's weaker physical side. In other words, Yanma's offensive prowess taking only stats into account puts the other 20 Speed Pokemon to shame. Yanma has natural bulk of 23 / 11 / 11, meaning Yanma does not excel in any particular defense but is well rounded- a trait no other 20 Speed Pokemon has. Diglett has BASE 10 HP, and although Elekid and Voltorb both have a passable SpD of 12, their lower HP than Yanma puts their bulk all around much lower. Yanma is therefore, without contest, the strongest and bulkiest of the 20 Speed Pokemon.
Bug / Flying Type: Bug types are desirable as some of the strongest Pokemon in the metagame are weak to Fighting-types, and Yanma's typing actually only makes it BETTER against Fighting-types. Yanma has a BST of 390 (and as shown above, those stats are in all the right places), while most Bug-types sit in the low - mid 200s, with the notable exceptions of Dwebble (low 300s) and Larvesta (360). BST is not enough to simply break a Pokemon, but the offensive prowess combined with the Speed of Yanma are definitively unrivaled not even just among Bug-types, but among the entire tier. Stealth Rock is a downfall, yes, but even broken Pokemon can have their cons. One entry hazard that became exceedingly less common this generation is not enough to justify something staying in the metagame, but if it is, I'm excited to see Ho-Oh in LC here pretty soon.
The final argument against Yanma is my original definition: "defeats or overcomes opponents with superior strength". One thing is Yanma has an accurate Sleep-inducing move 2 attacking options with side effects that help it do just that: overcome the opponent. One thing about Rest Sleep Talk Munchlax is that you actually gain a lot from putting it to sleep, as it can no longer use Rest to heal itself; the rest of the team can then find a way to muscle through it. So the proposed "counter" to Yanma is actually taken advantage of by Yanma, especially U-turn variants which will also deal a notable bit upon switching out. Other good examples are all of the other walls you mentioned, such as Vullaby, where it takes just one SpD drop from Bug Buzz or a flinch from Air Slash to be enough to cause it to be "overcome" by Yanma (also note Yanma can put Vullaby to sleep). This is the problem with Yanma (especially Compound Eyes): you simply cannot prepare well enough to face it. As things that are "counters" necessitate you to either give up momentum at best or simply lose to the Speed Boost variants late at worst.
NOW, I'd like to briefly touch on the suspect system, because it seems a few people here are slightly misunderstood. Tiering was done in a very, VERY problematic way in Gen V in that it never remained constant. At one point, one suspect test banned an unprecedented four things in Gligar, Meditite, Carvanha, and Misdreavus at one time, which led to the metagame basically collapsing for a few months while people actually tried to figure out what to use. This unprecedented event was followed by another; amidst a seemingly balanced metagame 6 months later, our LC tiering leader simply decided to unban Murkrow, Misdreavus, and Gligar. This, as intended, shook up LC, but steered the tiering process amiss forever as we were only to wonder what would've happened had the system continued regularly. Put simply, it made sense to TRY AGAIN this gen. Gen V had the stigma of being balanced but boring; we want to see if we can attain a metagame that is balanced and fun. The easiest way to do this is not start with last gen's banlist and try unbanning things (that's quite, QUITE difficult to do in a manner that is objective and healthy for a metagame, as people overuse the thing we unban), but to allow all Pokemon + Berry Juice and see which ones our system agrees with the last on being broken and which ones we find are not. What makes it different are two things: the ladderers are not the ones voting entirely as there is a council (this is important as it prevents people with agendas from having votes such as preventing avid ladderers from protecting their favorite broken strategy or banning ones they simply don't like) while also providing some means of consistency. Perhaps you are correct an and we will reach the same conclusions as last gen. I would say it is highly unlikely, and if even one mon that was "broken" in last gen stays because we find it's fine in this one, we've attained a "better" metagame.