While I myself would be somewhat open to the idea of re-evaluating Cloyster's rank in the metagame, I must disagree with your methodology behind its move, given that it is positively fallacious and idealistic. What I would gather from your post is that the situation in which you are addressing Cloyster's match-up with other Pokemon in the tier is based on the ideas that:
To begin, I must ask, under what circumstances is it so commonplace for Cloyster to find a window for set-up so easily? Entry hazards aside, I can assure you that no good player will concede so much breathing room to a potentially dangerous sweeper such as Cloyster if they lack a thorough check or counter to follow it up, and as physically bulky Cloyster is naturally, it doesn't exactly lend itself to multiple set-up opportunities; most Pokemon are capable of threatening significant damage to it in some way should it attempt set-up, either as a slower Pokemon capitalizing on its Defense drops to push significant damage or a faster offensive threat capable of hitting hard regardless. Cloyster folds to more-or-less any decently powerful special attack, or at the very least is significantly crippled, making its closest general set-up opportunities against more defensively oriented, physical attackers (Hippo, Lax, etc.), and by the nature of these Pokemon they are very commonly being paired with something that does handle Cloyster comfortably, such as Suicune or Slowbro, so very few teams immediately fold to it as you would let on.
Furthermore, the means you address these individual Pokemon seems to suggest a limited understanding of applicable scenarios. I'm all too sure a +2 Rock Blast from Cloyster OHKOs Mega Houndoom, but I would have to question the mindset of a player attempting to check a +2 Cloyster with a Mega Houndoom in the first place. A more relevant scenario would perhaps be something to the effect of whether or not Cloyster is capable of setting up against Mega Houndoom (which it cannot, for fairly obvious reasons), as it bears in mind Mega Houndoom's primary function in the tier, rather than on its ability to take hits. Against more defensively oriented Pokemon, these 'calcs' and so forth are relevant, as they will be combatting Cloyster in a defensive manner, so it is worth noting how well Cloyster can set up on and thereafter take on them. However, I am somewhat confused in reading this, as it at times will suggest that Cloyster has already been set up, then later it will not. That or these points are simply filled with misinformation, such as Choice Scarf Darmanitan outpacing a +2 Hasty Cloyster, though even then there are certain bits of misinformation (ie.Kyurem being unable to hit Cloyster?). That said, many of these calcs hold very little relevance in application.
That all being said, as an advocate of Cloyster, I feel it to be perfectly fine as it is in A rank. While an excellent win condition for offense, finding a moderate amount of set-up opportunities against softer physical attackers and cleaning up nicely vs.offense with a little chip damage on certain Water- and Steel-types (as most priority does a pittance, even at -1), it will inherently struggle to break through commonplace defensive Pokemon without significant prior damage, and between its vulnerability to entry hazards and its limited special bulk or relevant resistances, it does struggle to find very many opportunities to set up. In this regard, the "opportunity cost" of Cloyster a little too high for a S rank Pokemon, or even an A+ one, requiring moderate support of some nature to yield solid, yet not entirely consistent, results.
- Stealth Rock, or perhaps even no hazards at all are in play (as you mention the possibility of Focus Sash within certain points)
- In addition to the previous point, Cloyster was also given a 100% free set-up opportunity, in which it was damaged neither in switching in or setting up
- That every Pokemon within this list will be played in reactionary measure, switching in after it has been set up (again, apparently at full) in attempt to counter it
To begin, I must ask, under what circumstances is it so commonplace for Cloyster to find a window for set-up so easily? Entry hazards aside, I can assure you that no good player will concede so much breathing room to a potentially dangerous sweeper such as Cloyster if they lack a thorough check or counter to follow it up, and as physically bulky Cloyster is naturally, it doesn't exactly lend itself to multiple set-up opportunities; most Pokemon are capable of threatening significant damage to it in some way should it attempt set-up, either as a slower Pokemon capitalizing on its Defense drops to push significant damage or a faster offensive threat capable of hitting hard regardless. Cloyster folds to more-or-less any decently powerful special attack, or at the very least is significantly crippled, making its closest general set-up opportunities against more defensively oriented, physical attackers (Hippo, Lax, etc.), and by the nature of these Pokemon they are very commonly being paired with something that does handle Cloyster comfortably, such as Suicune or Slowbro, so very few teams immediately fold to it as you would let on.
Furthermore, the means you address these individual Pokemon seems to suggest a limited understanding of applicable scenarios. I'm all too sure a +2 Rock Blast from Cloyster OHKOs Mega Houndoom, but I would have to question the mindset of a player attempting to check a +2 Cloyster with a Mega Houndoom in the first place. A more relevant scenario would perhaps be something to the effect of whether or not Cloyster is capable of setting up against Mega Houndoom (which it cannot, for fairly obvious reasons), as it bears in mind Mega Houndoom's primary function in the tier, rather than on its ability to take hits. Against more defensively oriented Pokemon, these 'calcs' and so forth are relevant, as they will be combatting Cloyster in a defensive manner, so it is worth noting how well Cloyster can set up on and thereafter take on them. However, I am somewhat confused in reading this, as it at times will suggest that Cloyster has already been set up, then later it will not. That or these points are simply filled with misinformation, such as Choice Scarf Darmanitan outpacing a +2 Hasty Cloyster, though even then there are certain bits of misinformation (ie.Kyurem being unable to hit Cloyster?). That said, many of these calcs hold very little relevance in application.
That all being said, as an advocate of Cloyster, I feel it to be perfectly fine as it is in A rank. While an excellent win condition for offense, finding a moderate amount of set-up opportunities against softer physical attackers and cleaning up nicely vs.offense with a little chip damage on certain Water- and Steel-types (as most priority does a pittance, even at -1), it will inherently struggle to break through commonplace defensive Pokemon without significant prior damage, and between its vulnerability to entry hazards and its limited special bulk or relevant resistances, it does struggle to find very many opportunities to set up. In this regard, the "opportunity cost" of Cloyster a little too high for a S rank Pokemon, or even an A+ one, requiring moderate support of some nature to yield solid, yet not entirely consistent, results.
