Don't post here too often, but been playing some ORAS and watching a lot of the games recently, so figured I would throw my two cents into the pot.
As AM and Vertex said above, Zard-Y is fine where it is in A.
Nothing really makes Zard-Y any better than it was before - it is still kept in check by Latios, Latias, Mega Latias, Mega Altaria, Talonflame, Mega Zard-X, Dragalge, and a couple other less noteworthy things. We all acknowledge the fact that sun boosted Fire Blast from Zard-Y tears through anything that it hits neutrally not named Chansey and the fact that Focus Blast + Solarbeam coverage is very helpful to pick off what Fire Blast cannot, but Zard-Y requires more team support than pretty much everything else in the metagame - so much that it has a specific archetype (Zard-Y + Pursuit+ Defog Lati or Spin Starmie + three that are usually similar as the team needs to check certain things - see Valentine's RMT if you're curious as the XY variants have various parallels to ORAS variants) dedicated to it while Zard-Y doesn't function too well outside of this type of team. A Pokemon in A+ like Keldeo, Landorus-T, Garchomp, etc. can easily be fit into many teams regardless of the structure (obviously you won't throw a random Keldeo onto a stall team, but outside of that they're pretty universal) despite having a fair amount of checks or counters. Zard-Y isn't being slapped onto many teams without the aforementioned support as it needs Pursuit support to not be deadweight against many teams and it is 4x weak to rocks. Given the fact that Zard-Y has a fair amount of checks and counters while needing lots of support to prosper in the current metagame, it falls short of A+ rank and belongs just below it in A rank.
Regular Metagross should rise from D to C or C+.
It currently resides in D rank which is classified as:
D Rank: Reserved for Pokemon that hold a low amount of viability. Their positive traits are normally hindered by their negative traits.
Obviously regular Metagross has a limited niche given that it: A) only has one noteworthy set, in AV, to my knowledge, B) doesn't wall a substantial portion of the metagame or even special attackers in the tier with AV due to its typing and speed, and C) often is not worth using in teambuilding as special tanks like SDef Skarm, Ferro, Mixed Def Clef, Jirachi, etc. are all fairly common. However, it has seen use in various higher level matches lately (one of Shake's WCOP games and one of Tesung's WCOP games) and this is for a good reason - Meta can wall/trap Latis, act as a stop to common fairies like Clefable, Mega Diancie, Mega Garde, etc., annoy some other threats like Tornadus-T, Mega-Alakazam, Mega-Venusaur, Serperior, KyuremB, etc., and still maintain a fair offensive presence (meaning the negative traits don't often outweigh the positives which should be the case for D ranked Pokemon).
It should rise to C or C+ because it has a practical use and has been seen on solid teams while Pokemon in D and C- rank are almost always outclassed or obsoleted (examples: Mega Camerupt is way too slow to warrant using it, especially when it wastes the mega slot, as an SR user or special attacker when there are various common SR grounds and offensive fire types in the tier, Jellicent is far too passive and slow for a Pokemon vulnerable to knock off to function when there are plenty of Keldeo checks and utility Pokemon viable, and Chandelure being SR weak, frail, and slow makes it inferior almost every special attacker out there in comparison - Metagross has flaws, but it has a distinct niche and more viability than any of these). Pokemon with limited utility - defensively or offensively - like Cobalion, Seismitoad, etc. that reside in C+ have a comparable amount of viability to Metagross, in my opinion. Given all of this, regular Metagross should rise to C+ or at least C.
Tangrowth should rise from B- to B.
I don't think many people use Tang, although I could be mistaken, but it's an exceptional AV user that offers a lot to balanced or bulkier teams. The first pro of Tang that stands out to me is its movepool and offensive presence; Leaf Storm, Giga Drain, Hidden Power (fire usually), Sludge Bomb, Knock Off, Rock Slide, Earthquake, and even some other moves like Focus Blast can easily find their way onto Tang's moveset depending on what you need it to hit on the team it is being used on (I personally use Leaf Storm / Knock Off / HP Fire / Sludge Bomb). It has 100 base attack and 110 base SAtk which allow it to not be too weak despite usually not being invested in offenses due to need for SDef investment, too, so with this coverage and the defensive capabilities of Tang, which I will mention later, it is a pain to switch into at times and it is a pain to kill for many teams.
Defensively speaking, you need to invest in SDef with AV to let you check a lot of special attackers still, but with investment and naturally high HP+Def, Tang makes it work. Regenerator is a godsend, although it still appreciates hazard removal and even wish or cleric support, as it can maximize Tang's survivability despite it being unable to use a recovery move. Going into the specific defensive niche it has, Tang can switch into a lot of things without taking too much such as Keldeo, Excadrill, Garchomp, LandoT, Rotom-W, Raikou, unboosted Manaphy (even lives a +3 Ice Beam when healthy, but generally not a reliable counter in the long term), and even Latis (Draco does a fair amount, but not enough to break it and then it's forced out or gets Knocked Off) - it does match up poorly with quite a few common threats and I acknowledge this, but it also functions very well when dealing with the a plethora of threats, mainly those I just mentioned.
The defensive or tanky pokemon in B rank tend to have a niche in checking a fair amount of threats, but also having noteworthy flaws that prevent them from being top tier walls - this same classification can be applied to Tang. For example, Tentacruel can spin and check things like Keldeo and resist fairy, but it tends to be a bit frail on the physical side and is usually back-seated for Starmie as a spinner, Zapdos can also get rid of hazards, but it lacks the ability to withstand a lot of hits (almost all offensive A or S rank pokes can 2hko it) and is SR weak, etc. The defensive or tanky pokemon in B- tend to have more blatant flaws or drawbacks that seriously detract from their viability - Conk is too slow and weak to break things while it's vulnerable defensively even with AV, Mandibuzz has a hit or miss defensive typing and is SR weak, and Sylveon is typically in the shadow of Clefable while the specs set is hardly used seriously as far as I know. Tangrowth fits well with the B rank pokes and given its effectiveness, I think a rise is warranted.
