Right then, time to talk about these Ground-types.
Flygon (A-) -> B | Meru has already listed most reasons why Flygon should drop, but I'd like to add a few things. First of all, Flygon has the niche of being a Levitating, SR-resistant Defogger, but there's almost no other reason to use Flygon over Hydreigon. Flygon's 100 Attack is just disappointing compared to the myriad of physical powerhouses such as Heracross, Honchkrow or Lucario. As a mixed attacker, Flygon is outperformed by Infernape and, again, Hydreigon, who even sports superior bulk in 92/90/90 compared to Flygon's 80/80/80. Despite being a few points faster than Hydreigon, it's a vastly inferior Scarfer simply due to being unable to really hit hard. 100 Attack just doesn't cut it. Being a physical attacker, it's also highly susceptible to being burned, which makes it complete deadweight.
Overall, I feel like Flygon is really underwhelming as a whole and I really don't see it being in the same rank as things like Azelf, Roserade and the freaking Nidos. Flygon for B.
Hippowdon (A-) -> Remain A- | Kind of torn on this one. Hippowdon's a fantastic mixed and physical wall, but the reason why I'm not sure this thing should rise is simply the hostility of the UU metagame towards it. OU is a much more welcome territory for Hippowdon, but in UU it can still definitely pull its weight. Its 108/118/72 bulk is simply gigantic, especially on the physical side, which is what mainly allows Hippowdon to be so effective as a mixed wall. Ground-type STAB in Earthquake backed up by 112 Attack is pretty darn good and with Stone Edge or Ice Fang for coverage, Hippowdon is able to check most Pokémon that attempt to stand in its way. Sadly, the large myriad of Water- and Grass-types in UU ruin Hippowdon's walling potential, Slowbro being the prime example, as it's able to tank all those Earthquakes and just Slack Off all the damage, but repeated Crunches can drop Slowbro's Defense, so it's gotta be careful around those. Suicune can similarly take everything Hippowdon throws at it and offensive variants just OHKO with Hydro Pump. All Water-types (except Alomomola) can hit hard with Scald and burn it, while Roserade can just Grass Knot Hippowdon at its leisure. Roserade needs to watch the fuck out for Earthquake with its poor physical bulk, though.
In short, Hippowdon does have its shortcomings, but it's got a way around most of 'em and it's still as solid a wall as ever before. Keep Hippowdon in A-.

Overall, I feel like Flygon is really underwhelming as a whole and I really don't see it being in the same rank as things like Azelf, Roserade and the freaking Nidos. Flygon for B.

In short, Hippowdon does have its shortcomings, but it's got a way around most of 'em and it's still as solid a wall as ever before. Keep Hippowdon in A-.