Again, Mach Punch priority destroys Aerodactyl since its Rock typing offsets its Flying type, as well as the fact that Aerodactyl has no access to priority Flying type moves worth using. No other Grass/Fighting type has the utility Breloom does.

Let's take a look at the damage calculator.

Here is the calculation for Breloom's mixed attack set versus Aerodactyl's best defensive set: a lead with 252 Defense.

Low Sweep: 75.74 - 89.03%
Focus Punch: 125.91 - 148.5%
Bullet Seed: 93.68 - 111.62%
Stone Edge: 112.29 - 132.22%

252 Atk Choice Band Breloom Focus Punch vs. 0 HP / 252 Def Aerodactyl: 379-447 (125.91 - 148.5%) -- guaranteed OHKO

Now, that damage calculation was against Aerodactyl's best defensive set. Here's what the damage calculation looks like for the two 'meta' sets.

Focus Punch: 190.36 - 224.25%
Seed Bomb: 101.66 - 119.93%
Mach Punch: 76.07 - 90.03%

252+ Atk Choice Band Breloom Focus Punch vs. 0 HP / 0 Def Aerodactyl: 573-675 (190.36 - 224.25%) -- guaranteed OHKO

The only real absolute check to Breloom is Celebi; Gengar, Amoonguss, and even Latias can be taken down by different variants of Breloom's many possible sets.

So there you have it.