From what I gathered from
Porygon 2 For A-Rank
Look I'm not going to make this more complicated than it should: Porygon 2 is simply one of the metagame's best walls which is only really hindered by one thing: the *good* fighting types in UU. And it can actually take a hit from most of them bar something like LO Mienshao HJK or CB herra's CC(which for the most CB herra isn't even viable, scarf is the way to go. also I believe CB Herra barely manages the kill with CC after SR, someone correct me if I'm wrong). But despite it's one noticable flaw, it's still an amazing wall! not only can this thing go as a special wall but it can serve as a physical wall (which trust me the physicaly defensive set (not on smogon yet I don't think) is a monster to deal with as it para's and recovers in the front of all your sweepers) and a possible mixed wall! But for the most part i'm going to bring up the mixed wall AKA Smogon's "Defensive Duck" Set for it's defensive discussion.
Alright first lets dive into it's great job as a wall: It can wall most of the metagame's sweepers and well, it's up to you whether you para them and slowly chip them while recovering with twave + recover , or slowly stall with toxic+ recover, either way you'll annoy the crap out of the opposing sweeper and possibly take them down. And this thing can actually take hits from A LOT of fighting types, especially the standerd sets. (case and point:
252 Atk Heracross Close Combat vs. 252 HP / 176+ Def Eviolite Porygon2: 56.68 - 67.37% ,
252 Atk Scrafty Hi Jump Kick vs. 252 HP / 176+ Def Eviolite Porygon2: 49.73 - 58.28% etc) as you can see from those calcs, the standerd defensive duck set is no joke when it comes to taking physical hits, and of course as porygon users know, isn't a joke on the specially defensive side. Now that's half of my arguement for the defensive side since I feel like people are going to argue against me, which is fine but I don't feel like restating myself so I'll simply save the rest of my arguement on it's defensive side.
Now you maybe thinking: HURR PORY CAN NEVER GO OFFENSIVE SO IT LOSES TO WALLS LIKE EMPOLEN THAT CAN.(I know I mispelled Empoleoon, that was on purpose): Enter: Duck Tank/Offensive Porygon. This thing has so much going for it, not only does it simply demolish usual porygon2 stoppers but it allows this thing to have an actual offensive presance, now if you don't believe me lets look at some calcs (counting download):
252+ SpA Porygon2 Tri Attack vs. 0 HP / 4- SpD Raikou: 136-162 (42.36 - 50.46%) -- guaranteed 2HKO after Stealth Rock and Spikes(standerd sub CM)
+1 252+ SpA Porygon2 Thunderbolt vs. 252 HP / 4 SpD Suicune: 260-306 (64.35 - 75.74%) -- 87.5% chance to OHKO after Stealth Rock and Spikes(CroCune)
+1 252+ SpA Porygon2 Tri Attack vs. 0 HP / 4 SpD Mienshao: 279-328 (102.95 - 121.03%) -- guaranteed OHKO
+1 252+ SpA Porygon2 Tri Attack vs. 0 HP / 4 SpD Scrafty: 163-193 (60.14 - 71.21%) -- 6.25% chance to OHKO after Stealth Rock and Spikes(these should all really be accounted for as switches)
etc. etc. The list goes on with what pory2 could do with this set, and it's defensive side is not too bad, just don't be hoping to tank a CC.
And that's the end of my request for Pory2 to A rank, if it's needed I'll elaborate on both of the types of Pory2 sets and how they are effective in this current UU metagame.
From what I gathered on your paragraph, I'd like to address a few things. And I'm gonna focus on the point that I don't think Porygon2 is really an A-Rank Pokemon. Granted, P2 is annoying and a nightmare for teams lacking either a Toxic user or a powerful fighting-type, a lot of your post seems really slanted against the very logic of why Porygon2 is in B-Rank in the first place. First off, you mentioned "Good" fighting types in UU. Cobalion isn't good? Virizion isn't good? The worst Porygon2 can do to a Cobalion is paralyze it with thunder wave while letting it either A) Setup an SD, B) Go for a Close Combat, or in the super duper rare case, C) It sets up a sub and starts spamming Calm Mind as you switch. Same deal with Virizion, Porygon2 can at least Ice Beam it, but it has access to Calm Mind and a high SpDef stat to make this somewhat negligible.
Two, CB Heracross rapes every variant of Porygon2 you can conjure up, no questions asked. Don't believe me?
252+ Atk Choice Band Heracross Close Combat vs. 252 HP / 252+ Def Eviolite Porygon2: 324-384 (86.63 - 102.67%) -- 18.75% chance to OHKO
^ The above calc is an exaggeration, as no one that I really know of has really popularized a full-on physically Defensive Porygon2 , which is exactly why it isn't on Smogon. But the point is, if Band heracross has a chance to OHKO a full physically defensive Porygon2 from full HP, then why try to ride so hard that it can deal with Fighting-types such as it? Sure, it can status Heracross. ...And possibly activate Guts. Some variants of Scarf Hera even run Guts on rare occasons, and add that to the fact that it just steps up however much damage it's already doing and basically Porygon2 is a dead duck.
You also mentioned it can wall most of the metagame's sweepers. While to some extent this is true, I'm not gonna take time to list every sweeper it can beat out, but I will say that it's not stopping things such as: SubCM raikou, Swords Dance Heracross (This is also a thing you seem to have forgotten the existence of), Specs Shaymin, etc. On top of that, if Porygon2 gets Toxic'd, it becomes incredibly easy to wear down over time and can't counter stall the opponent with Recover.
And as for the calcs on the offensive Porygon2 set, you chose some optimally convenient situations to post calcs for...First of all, the calc you did on Raikou was a Rash Raikou. Standard SubCM Raikou runs Timid, so it wouldn't have a lowered SpDef stat. Granted on top of that, no one would instantly throw Raikou at a Porygon2 unless they were predicting an electric move, in which case you also can't totally account for Spikes (and even Stealth Rock half the time) being up on your side of the field in every scenario. Raikou could take any move, get a +1 up, and go from there while you're just sitting there blowing Tri Attacks off. The calc you did on Mienshao, Reckless Hi Jump Kick would OHKO a Porygon2, and even moreso assuming the fact it's the Duck tank which has less bulk. You said to assume the opponent switched their Pokemon in on Porygon2 in each of those scenarios, meanwhile Suicune, and maybe Raikou, is possibly the closest most relevant switch-in of all the sets you listed, all of which aren't even incredibly bulky sweepers. (PS, no one would switch in Mienshao on a Porygon2. It dies to a stiff breeze, let alone most powerful hits. Why factor in a calc on it?) I feel you're really slanting your opinion of Porygon2 when you're overlooking some simple facts:
1. Like I said, Toxic ruins Porygon2. If it gets badly poisoned and you have no cleric support, P2 becomes more of a liability for the opponent to take advantage of, add that on top of hazards and the lack of passive recovery.
2. Did I mention the lack of passive recovery? Some calcs you mentioned Porygon2 is 2HKO'd by some things up above. Unless you're carrying Thunder Wave and spamming recover afterward, then you may as well just accept the fact Porygon2 is dying the subsequent turn because it's not gonna be healing off of that without using Recover and giving the opponent another free turn.
3. Porygon2's also highly susceptible to Trick. If it's stripped of its eviolite and even moreso given an item it can't even use, like Choice Scarf, Porygon2 is now deadweight, no questions asked. I mean, if someone tricks it a Specs, then maybe it can be a problem, but...It dies even more easily than it did before without its item. I won't even talk about how easy it is to play around when it's locked into one move.
4. It's not standing up to the fighting-types in this tier, whether you consider them or their sets relevant or not. Throwing a Porygon2 at any Heracross is just folly, whether you think it can take it on or not. Throwing it at a Mienshao, Scrafty, Cobalion, Virizion, or even a freaking Hitmontop half the time is gonna just end up costing you a Pokemon as a result. Play to its strengths rather than try to minimize its weaknesses.
All these reasons are exactly why Porygon2 is coolin' in B-Rank. I actually do love Porygon2 and it has potential to be a versatile Pokemon, but it's not more than what it already is.