Call me crazy but I disagree with moving Mega Aero up to S. Despite how the metagame favours its existence, it still has a lot issues. A 135 base attack and Tough Claws with the ability to go Adamant for more power seems really good, especially with a colourful movepool that gives it Water, Fire, Dark and Ground etc. coverage. However, most of his contact moves except a few like Aqua Tail and Crunch have extremely low BP thusly offsetting the Tough Claws boost, and that includes its own STAB Aerial Ace.
You do realize that Tough Claws is essentially a Life Orb boost without recoil, right? With this Ability, Aqua Tail has 120 BP and Crunch 104 BP, making them powerful enough to clean most of its threats. Regarding Aerial Ace, let's see how much power it has. 60*1.5 = 90 -> 90*1.3 = 120, which is the same as a STAB Crunch. The Elemental Fangs have a respectable 86 BP, which
really isn't as bad as you make it out to be. What makes Aerial Ace such a good move on Mega Aerodactyl is its Flying-type, which shreds common threats like Infernape, Mienshao and especially Heracross, one of the most major offensive threats in UU at the moment. It then has a powerful STAB Stone Edge at its disposal, while having coverage in Earthquake. Add SR support and Mega Aerodactyl will always be able to pull its weight as an offensive Pokémon. Its moves are not as weak as you make them out to be, since Aqua Tail and Crunch are often run, while it's usually only one Elemental Fang, not all three of them.
While it gets some really nice utility moves such as Pursuit, Defog, Taunt and Stealth Rock, it is more of a jack of all trades master of none and it can't run all of those moves at once without losing precious coverage or Roost (which is really important as it is weak to rocks and has to check many things). It also loses out on U-turn, a move that it would kill for so it can preserve momentum or breaking Alakazam's sash without taking a hit.
Pursuit and Stealth Rock are two support moves that set Mega Aerodactyl apart from Crobat. Not to mention, thanks to its base 135 Attack, Mega Aerodactyl can deal a larger deal of damage with Stone Edge than Crobat can with Brave Bird on defensive sets.
And yes, while it is very versatile being able to run many sets, all of them shares similar checks and counters like Swampert and Mega Aggron which Aerodactyl just fails to scratch, unlike other S-rank offensive threats such as Victini/Hydreigon who has a wide movepool and mixed offensive stats to muscle past most if not all of their checks and counters, wheras Heracross's extreme brute force allows it get past even Granbull with an SD GutsOrb set or at least cripple them with Knock Off. Again, due to its lack of U-turn you are almost always forced to sacrifice momentum when it gets hard countered which is a real pain for offensively based teams.
Hydreigon and Heracross are hardwalled by Fairy-types, yet they're still S-Rank. Slowbro is countered by Hydreigon, but it's still S-Rank. Blissey is shat all over by Taunt users such as Crobat and Mega Aerodactyl,
but it's still S-Rank! If we take a look at OU, Keldeo is S-Rank, but it has a share of hardcounters nonetheless. If we take a look at RU, Zoroark is S-Rank, but is hardwalled by Aromatisse most of the time. In short,
hardcounters are not a valid argument for a Pokémon not to be S-Rank. I should also note how every S-Ranker outside of Blissey has four or five weaknesses, just like Mega Aerodactyl:
- Hydreigon is weak to Dragon, Fighting, Bug, Ice and
Fairy.
- Slowbro is weak to Electric, Grass, Bug, Ghost and Dark.
- Heracross is weak to Fire, Fairy, Psychic and
Flying.
- Victini is weak to Water, Rock, Ground, Ghost and Dark.
- Mega Aerodactyl is weak to Ice, Electric, Rock, Steel and Water.
See? These weaknesses don't deter the first four from being S-Rank, so it shouldn't deter Mega Aerodactyl from this position, either.
That is not to mention the flaws that every Mega Evolution shares such as no passive lefties recovery, needing a turn to Mega up to get the speed/bulk and inability to employ another Mega. Keep Maero at A+
Before Mega Evolution, Aerodactyl has 105 Speed, which really isn't as bad as you're making it out to be. Even after Mega Evolving, it's still outsped by Scarfers, but that extra bulk allows it to live a hit and strike back hard with its boosted Attack stat and Tough Claws. The fact that another Mega Evolution can't be used applies to
every Mega Evolution ever. A Mega Evolution is chosen depending on what the team requires, not the other way around.
Mega Aerodactyl fully deserves to be S-Rank for the insane amount of Pokémon it checks and due to its amazing offensive prowess and valuable support.