Not to mention the most common OU Fighter is part Steel (Lucario); Fire/Psychic also fails against Houndoom.
Rock, Ice and Dragon are all resisted by Steel and are the best attacking types...or not? On October 2008, Fire was the most common offensive type in OU, and it would be even more common with Scizor's increasing poplarity...
Rock, Ice, Dragon, and Dark are all types that fail to hit Steel Super Effectively but have no Pokemon immune to them. They are also largely unresisted by non-steel types, meaning each of these types can be paired with a type that hits Steel for near-perfect coverage. Fighting has almost perfect coverage with any one of those types (Fighting/Dark misses on one OU Pokemon). Ground has nearly prefect coverage with any one of those types (except on Bronzong/Skarmory, and Flygon/Breloom for Rock). Water has nearly perfect coverage with any one of those (except on Empoleon), except Ice which fails on pure water types. Etc. None of those types can really be used without a type that can hit steel, but those types that can hit steel really need the aid of one of these.
Is Bug a good offensive type? Is Dark bad defense? Is Icw worst defense? Is Poison good defense?
Bug is probably one of the worst offensive types. There are only 2 Dark Pokemon and 2 Grass Pokemon in OU (one of which is neutral to Bug), and a grand total of 6 types resist it, including the omnipresent Steel. This means that it is nearly impossible to pair Bug with a single type to have good Neutral coverage. There is a reason why you rarely see Pokemon packing a Bug move for coverage (with the exception sometimes of Psychics, who pack signal beam to both hit other Psychics and Dark types). U-Turn is used widely because of its ability, not the fact that it is Bug. If there were another option for the same effect, Pokemon would run that instead.
Dark is decent Defense. It resists both Dark and Ghost, which are commonly used to hit Ghost types, as well as being immune to Psychic, which allows for a lot of free Pursuit KOs. A weakness to Fighting hurts, but no type is without a weakness to a commonly used type.
Ice is probably the worst defensive type. It packs only a single resistance, albeit to a commonly used type, but it is also weak to three of the most used types in the game (Fire, Fighting, and Rock), which also gives it the quite unfortunate Stealth Rock weakness. Weakness to Scizor's Bullet Punch (the only really common Steel move) is just icing on its cake of badness.
Poison is decent defense. It provides a resistance to Fighting without being weak to to the coverage moves that fighting types usually pack (Ice, Rock, Dark, and Ghost). Bug, Grass, and Poison are all fairly uncommon attacking types, but it never hurts to have resistances to them. Psychic is a very rare attacking type, making that weakness almost non-existent, leaving it only with the unfortunate Ground weakness.
