Dragonite is not really terrible, but most of the things that Dragonite is good at, Salamence can do better. There are things that Dragonite can do that Salamence cannot, but they are mostly niche things. Dragonite has a wider movepool, but Salamence has more speed. Dragonite has better defenses, but Salamence has Intimidate. Salamence gets Wish, Dragonite gets Heal Bell. But most of the time, you'll be wanting a Choice Band or Dragon Dance set, and Mence does this better. There's no reason to use Dragonite when Salamence is available, unless you absolutely need the extra moves.
Ice Beam Ttar is really cool for people that use Flygon to cover you, but you'll be open to being statused or phazed by a lot of Pokemon without Taunt. I have never used Curse ttar, though, so I'm not sure how he plays.
Swampert plays different from other bulky waters because he trades water and ice resists for a rock resist and electric immunity. The rock resist is awesome, but the electric immunity is enough to make some Pokemon that would otherwise be monstrous (Raikou, for one) a lot less useful, because they need to run HPGrass instead of HPIce (or Fire). Ice or Fire are useful against a whole lot more Pokemon, but you run the risk of your opponent having a Swampert, and rendering your Pokemon 100% ineffective. And man, it's really hard to break a wall when it only has one weakness.
Steel types make great Rock resists until you realize that most rock sliders run Earthquake right next to it. Skarmory/Forretress are great, but there's always the Magneton threat. Swampert has the ability to take both of these, AND has two STABs that hit super effective against lots of quakesliders.
Swampert is awesome.
wrt Hydro Pump Salamence, you could run it, but why? What does it hit better than HPFly/EQ/Rockslide? Even on CBMence, I would rather use Fire Blast as a special attack, because again, what are you hitting that you can't hit with your other moves?
And to be honest, I agree about the CB/DD thing. I would rather take CB, because I like Ttar and Gyarados better as DDers.
On Metagross, I guess it's up to you what item to use. I like CB for the immediate power, and it's good for luring out Pokemon that are weak to electric types, due to how ridiculously hard it is to take a CB Meteor Mash.
Really? I agree about ttar celebi suicune, but is gar really that much better than everything else? It's dangerous, fast, unpredictable, and has great immunities, but the low defenses make it pretty vulnerable. It's a great Pokemon, don't get me wrong, but I wouldn't put it in the same class as the other three.