Without disagreeing with the entirety of your post: the problem with nominating Hippowdon as a check to Mega Gallade and Altaria is with the 'unboosted.' There aren't really that many circumstances where Hippowdon will get a free switch against a +0 Gallade or a +0 DDing Altaria, and both Pokemon roll over it handily with their requisite boosts. Actually, bulky DD Altaria handles Hippowdon even if it does get in a free switch at +0, taking 36% max from EQ. Special attacking variants also have possible 2HKOs with Hyper Voice.
Hippo roars them out with ease, specially defensive Hippo is not 2hkoed after SR
252+ SpA Pixilate Altaria Hyper Voice vs. 252 HP / 252+ SpD Hippowdon: 165-195 (39.2 - 46.4%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
and bulky DD needs alot of boosts to beat physcial defensive Hippo 100% of the time
+3 0 Atk Pixilate Altaria Return vs. 252 HP / 252+ Def Hippowdon: 238-282 (56.6 - 67.1%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Offenisve M-alt can 2HKO at +1 but I've never seen tat outside of low ladder play so idk how viable that is. Hippo also checks Gallade quite easily if it switches in on the SD or if Gallade attacks without boosting
252 Atk Gallade Close Combat vs. 252 HP / 252+ Def Hippowdon: 151-178 (35.9 - 42.3%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
Also the fact that it can wall both MegaGross and Zone is so amazing for balanced teams atm that there is no way that Hippo should not rise to
A-, Not to mention how well it fits in on many high ladder
shitty broken fuck Stall teams because of its ability to counter those two AND phaze other strong attackers like LumSD chomp, Mscizor, SpecsGengar and Lati@s with the same set. REliably recovery is amazing and Sand stream stops Rain. Outside of that I support the raise of both Breloom and Chesnaugh to
A- and
B+ respectivly. Im not sure about MegaPert becasue I never have a problem dealing with rain and never use them myself. I also think Camel and Bee should drop but thats pure theorymon, since they both struggle to do anything against offensive and Stall/Semi-Stall respectivly.
One mon I've been using a lot lately is non-mega Scizor. Dont get me wrong Mscizor is a monster against everything but Band Bullet punch is really good in the current meta against MAero, MAlteria and pretty much anything on HO. I can easily see it rise to
B+ because it is a pretty strong mon against HO and Balance and can work really good in a slow Volt-Turn core with Zone or an offensive one with Mega-Man, something which its mega cant (can do with Zone obv).
Some calcs:
252+ Atk Choice Band Technician Scizor Bullet Punch vs. 0 HP / 0 Def Altaria: 300-354 (103 - 121.6%) -- guaranteed OHKO
252+ Atk Choice Band Scizor U-turn vs. 252 HP / 252+ Def Slowbro: 254-302 (64.4 - 76.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Choice Band Scizor Knock Off vs. 0 HP / 0 Def Metagross: 166-196 (55.1 - 65.1%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Choice Band Technician Scizor Bullet Punch vs. 28 HP / 0 Def Gengar: 244-288 (91 - 107.4%) -- guaranteed OHKO after Stealth Rock
252+ Atk Choice Band Scizor U-turn vs. 4 HP / 0 Def Bisharp: 189-223 (69.4 - 81.9%) -- guaranteed 2HKO after Stealth Rock
-1 252+ Atk Choice Band Scizor Knock Off (97.5 BP) vs. 252 HP / 252+ Def Landorus-T: 90-106 (23.5 - 27.7%) -- 8.4% chance to 4HKO after Stealth Rock and Leftovers recovery
-1 252+ Atk Choice Band Technician Scizor Bullet Punch vs. 0 HP / 0 Def Landorus-T: 118-139 (36.9 - 43.5%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
252+ Atk Choice Band Scizor Knock Off (97.5 BP) vs. 0 HP / 4 Def Excadrill: 261-308 (72.2 - 85.3%) -- guaranteed 2HKO after Stealth Rock
252+ Atk Choice Band Scizor Superpower vs. 172 HP / 0 Def Magnezone: 382-450 (117.9 - 138.8%) -- guaranteed OHKO
Superpower can also boop Bisharp and Drill