What a Pokemon resists is better to determine if that Pokemon is good or not, imo. See Celebi, people would say that Grass/Psychic typing sucks because of all it's weaknesses but I rarely see anyone saying that it's good for all the things it resists.
When I hear people saying that Sableye/Eelektross have good typing because they don't have any weaknesses I kinda laugh in my head, those typings don't really resist anything important (Well Sableye is immune to Fighting so that's a plus)
Basically I just feel that when talking about if a typing is good don't focus so much about what it is weak to, focus more on what it resists.
Having more weaknesses means you get forced out more easily. With Celebi, you're very frequently going to be running into Pokémon that hit it for Super-Effective damage.
Resistances are helpful for switching into attacks, and occasionally forcing out Pokémon that can't hit them for 1x damage or more. So resistances aren't as helpful in Double Battles because one of the opposing Pokémon is highly likely to be able to hit you effectively, and it's more likely you can be hit for Super-Effective damage. Having a lot of weaknesses in a Double battle can be trouble, Abomasnow has had to get used to it.
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I feel people buy into weaknesses too much. I can't count how many times I've read "Hardy dar Gyarados sucks cuz it dies to spark." Yes, while electric attacks kill it, it resists many common types such as fire, water, bug, fighting, and Scizor's primary weapon and has an immunity to ground. Those are very nice things to have, but people get caught up into the electric weakness.
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Weaknesses are more important that resistances. It's why Shedinja still sucks even though it's immune to like 10 types..It's why even though Dragons are resistant to many things Ice pokemon can eat them for dinner.
If your pokemon is weak to a commonly used competitive type it stands no chance. It'll get one shotted.
Weakness = 2-4x damage
That is killer and when you have pokemon with high attack doing 2-4x damage, that pokemon is dead. IMO a pokemon with no resistances or weaknesses would be better than one with huge weaknesses to common offensive types.
For example, lets take an attack that would do "100 hp" damage.
1/4x resistance = 25 HP damage (75HP saved) 1/2x resistance = 50 HP damage (50HP saved) 2x weakness = 200 HP damage (100HP lost) 4x weakness = 400 HP damage (300HP lost)
See how a 4x weakness is absolutely crippling and modifies the amount of HP you take by a lot more than a 1/4x resistance? Resistance helps, but weaknesses cripple your pokemon and can make even high HP/defense pokemon get destroyed.