Well, I'll be the reverse of this and say that Manetric is not very good because his flaws out weigh his good points. He gets OHKOed by any Earthquake from any pokemon with good Attack. The only thing he has going for him is Intimidate, his speed, and Volt switch. other than that, It's only passable. I'll say c-, c at most.
You can't just say that it has a bunch of flaws, point out only one flaw, and declare it C rank just like that. Also to say that it dies to any Earthquake may be true for 252/252 M-Manectric but not for 100 Def/252 SpA/156 Spe. Ideally it will be partnered up with Landorus-T or Gyarados so it will never have to take these Earthquakes in the first place but here are some Earthquakes it survives after 100 def and Intimidate.
Garchomp
-1 252 Atk Garchomp Earthquake vs. 0 HP / 100 Def Mega Manectric: 234-276 (83.2 - 98.2%) -- guaranteed 2HKO
Salamence
-1 252 Atk Salamence Earthquake vs. 0 HP / 100 Def Mega Manectric: 160-190 (56.9 - 67.6%) -- guaranteed 2HKO
-1 252 Atk Life Orb Salamence Earthquake vs. 0 HP / 100 Def Mega Manectric: 208-247 (74 - 87.9%) -- guaranteed 2HKO
Terrakion
-1 252 Atk Terrakion Earthquake vs. 0 HP / 100 Def Mega Manectric: 156-184 (55.5 - 65.4%) -- guaranteed 2HKO
-1 252 Atk Choice Band Terrakion Earthquake vs. 0 HP / 100 Def Mega Manectric: 232-274 (82.5 - 97.5%) -- guaranteed 2HKO
Dragonite
-1 252+ Atk Dragonite Earthquake vs. 0 HP / 100 Def Mega Manectric: 174-206 (61.9 - 73.3%) -- guaranteed 2HKO
Gyarados
-1 252+ Atk Gyarados Earthquake vs. 0 HP / 100 Def Mega Manectric: 166-196 (59 - 69.7%) -- guaranteed 2HKO
-1 252+ AtkMold Breaker Mega Gyarados Earthquake vs. 0 HP / 100 Def Mega Manectric: 194-230 (69 - 81.8%) -- guaranteed 2HKO
Mega Charizard X
-1 252 Atk Mega Charizard X Earthquake vs. 0 HP / 100 Def Mega Manectric: 156-184 (55.5 - 65.4%) -- guaranteed 2HKO
252 Atk Mega Charizard X Earthquake vs. 0 HP / 100 Def Mega Manectric: 234-276 (83.2 - 98.2%) -- guaranteed 2HKO
Obviously there will always be some that it will never be able to take like Adamant Excadrill's, both Landorus formes, and
Diggersby tho but
every Earthquake? Come on nigga.