You are right about Kyogre. I know that steel doesn't resist electric type moves and that there are plenty of water types that can learn thunder-based moves. I make myself look like a fool with my knowledge of Pokemon... Anyway, back to topic.
It would make sense that pokemon with the ability to create storms would be able to learn Thunder and other moves like that. Thunder, like you said, is quick to follow after storms.
I've seen people with Skarmory in a battle video that are total powerhouses when it comes to defense. A skarmory with Roost is especially annoying, and sturdy doesn't make it any better. Even if it didn't have Sturdy, with it's defense, it could withstand a good amount of attacks and you could make it hold a Focus Sash (Focus band wouldn't work if it already took damage) Articuno could get creamed if you improved Skarmory's attack enough if you use Steel Wing. It wouldn't hurt if Skarmory could be able to use Metal Sound to lower defense.
Hydreigon reminds me of a Hydra... Wait, isn't that what it is based on? All pokemon are based on something, right?
Where did you hear that Electross lives underwater? If that really is true, it should be able to learn more water type moves than it currently can. Another thing is it can learn Flamethrower. It suprises me, some pokemon being able to use these moves when it has nothing to do with the pokemon (In Electross's case, it probably has something related to it)