The point is that azumarril outclasses crawdaunt in almost every role due to its far better bulk. Now lets stop with this pointless circlejerk and get back to finding what crawdaunt can do to differatiate itself from others without getting outclassed.
Don't say Azumarill is better outright and then try to drop the argument, that's the worst.
Anyway, lets see what that 20% does.
Aegislash is big, right?
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Aegislash-Shield: 238-282 (73.4 - 87%) -- guaranteed 2HKO
252+ Atk Choice Band Huge Power Azumarill Crabhammer vs. 252 HP / 0 Def Aegislash-Shield: 210-247 (64.8 - 76.2%) -- guaranteed 2HKO
10% difference. With two layers of hazards, Aegislash might get OHKO'd. Still, not a huge deal, 2 layers isn't big. Knockoff however definitely kills Aegislash. So against Aegislash, Crawdaunt probably wins out.
Rotom Wash...
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Rotom-W: 160-189 (52.6 - 62.1%) -- 98.8% chance to 2HKO after Leftovers recovery
252+ Atk Choice Band Huge Power Azumarill Waterfall vs. 252 HP / 0 Def Rotom-W: 112-132 (36.8 - 43.4%) -- 99.4% chance to 3HKO after Leftovers recovery
There's difference A- a 2hko on Rotom Wash. Granted, neighter is going to stay in on Rotom wash, but the potential to kill a half off offensive rotom is nice. Of course, their secondary STABs are 2HKOs as well.
Ferrothorn...
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Ferrothorn: 135-159 (38.3 - 45.1%) -- guaranteed 3HKO after Leftovers recovery
252+ Atk Choice Band Huge Power Azumarill Waterfall vs. 252 HP / 0 Def Ferrothorn: 94-111 (26.7 - 31.5%) -- 27.2% chance to 4HKO after Leftovers recovery
Not great either way, but the difference is clear. At least Crawdaunt can do a 2hKO with knockoff, though.
Talonflame gets Aqua jet Calcs
252+ Atk Choice Band Adaptability Crawdaunt Aqua Jet vs. 252 HP / 0 Def Talonflame: 360-428 (100 - 118.8%) -- guaranteed OHKO
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 252 HP / 0 Def Talonflame: 318-374 (88.3 - 103.8%) -- 31.3% chance to OHKO
Hey, that's important! So long as people are still running max hp talonflame.
MegaKang
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Mega Kangaskhan: 340-400 (82.1 - 96.6%) -- 62.5% chance to OHKO after Stealth Rock
252+ Atk Choice Band Huge Power Azumarill Play Rough vs. 252 HP / 0 Def Mega Kangaskhan: 268-316 (64.7 - 76.3%) -- guaranteed 2HKO after Stealth Rock
Also significant, although who switches Kang into an attacker, really
TTar gets screwed on the switch, but if it's just Aqua Jets-
252+ Atk Choice Band Adaptability Crawdaunt Aqua Jet vs. 0 HP / 0 Def Tyranitar: 252-300 (73.9 - 87.9%) -- 6.3% chance to OHKO after Stealth Rock
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 0 HP / 0 Def Tyranitar: 218-260 (63.9 - 76.2%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Crawdaunt does slightly better against an offensive variant
Klefki
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Klefki: 368-434 (115 - 135.6%) -- guaranteed OHKO
252+ Atk Choice Band Huge Power Azumarill Waterfall vs. 252 HP / 0 Def Klefki: 258-304 (80.6 - 95%) -- 12.5% chance to OHKO after Stealth Rock
Significant.
Scizor
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 0 Def Scizor: 340-400 (98.8 - 116.2%) -- guaranteed OHKO after Stealth Rock
252+ Atk Choice Band Huge Power Azumarill Waterfall vs. 252 HP / 0 Def Scizor: 238-282 (69.1 - 81.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
That's... a big deal, actually.
Mamoswine
252+ Atk Choice Band Adaptability Crawdaunt Aqua Jet vs. 252 HP / 0 Def Mamoswine: 328-388 (77.3 - 91.5%) -- 31.3% chance to OHKO after Stealth Rock
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 252 HP / 0 Def Mamoswine: 288-342 (67.9 - 80.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
also a big deal.
Gengar
252+ Atk Choice Band Adaptability Crawdaunt Aqua Jet vs. 0 HP / 0 Def Gengar: 206-244 (78.9 - 93.4%) -- 37.5% chance to OHKO after Stealth Rock
252+ Atk Choice Band Huge Power Azumarill Aqua Jet vs. 0 HP / 0 Def Gengar: 180-213 (68.9 - 81.6%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
Beating Gengar a third of the time? I'll take it.
And the bane of all physical, Sableye:
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 252 HP / 252 Def Sableye: 322-380 (105.9 - 125%) -- guaranteed OHKO
252+ Atk Choice Band Huge Power Azumarill Waterfall vs. 252 HP / 252 Def Sableye: 226-267 (74.3 - 87.8%) -- 6.3% chance to OHKO after Stealth Rock
SO, yes, that 20% does make a difference in a lot of cases. If you wanted a pokemon to sit there and launch Priority and massive hits... Crawdaunt does a pretty good job. He just takes less hits and delivers bigger hits.
Anyway, onto differences- Knockoff vs playrough
Both are good, but Knockoff is fantastic. That's basically it.
Crawdaunt also has the option of dragondancing, making it a true monster and a sweeper, something Azumarill can't hope to achieve.
So. Crawdaunt has some nice OHKOs with a band that Azumarill can't touch, and the option to DD, where Azumarill has bulk.