In my OPINION, Goodra is underrated because of its decent Def Stat and its Speed: weak against Garchomp, Salamence and Dragonite.
252 Atk Garchomp Dragon Claw vs. 252 HP / 0 Def (custom): 354-416 (92.18 - 108.33%) -- guaranteed OHKO after Stealth Rock
252 Atk Salamence Dragon Claw vs. 252 HP / 0 Def (custom): 360-426 (93.75 - 110.93%) -- 62.5% chance to OHKO
252+ Atk Dragonite Dragon Claw vs. 252 HP / 0 Def (custom): 392-464 (102.08 - 120.83%) -- guaranteed OHKO
Now, if Goodra has 252 HP/252 Def with its beneficial nature:
252 Atk Garchomp Outrage vs. 252 HP / 252+ Def (custom): 356-420 (92.7 - 109.37%) -- guaranteed OHKO after Stealth Rock
252 Atk Salamence Dragon Claw vs. 252 HP / 252+ Def (custom): 242-288 (63.02 - 75%) -- guaranteed 2HKO
252+ Atk Dragonite Dragon Claw vs. 252 HP / 252+ Def (custom): 266-314 (69.27 - 81.77%) -- guaranteed 2HKO
Now, if we put my previous movesets, with +6 in Defense and 252 HP/252 Sp. Def:
252 Atk Garchomp Dragon Claw vs. +6 252 HP / 0 Def (custom): 90-108 (23.43 - 28.12%) -- guaranteed 4HKO after Stealth Rock
252 Atk Salamence Dragon Claw vs. +6 252 HP / 0 Def (custom): 92-110 (23.95 - 28.64%) -- possible 4HKO
252+ Atk Dragonite Dragon Claw vs. +6 252 HP / 0 Def (custom): 102-120 (26.56 - 31.25%) -- guaranteed 4HKO
252 SpA Choice Specs Latios Draco Meteor vs. 252 HP / 252+ SpD (custom): 372-438 (96.87 - 114.06%) -- 81.25% chance to OHKO
252 SpA Choice Specs Latias Draco Meteor vs. 252 HP / 252+ SpD (custom): 330-390 (85.93 - 101.56%) -- 12.5% chance to OHKO
As you can see, Acid Armor can work perfertly with it if it used correctly, Toxic and Infestation will cripple attackers and rest to heal! But Salamence, Dragonite and the eons pokémons are, and still, the counters (lol sableye).