Flygon won't be sweeping Lance any time soon, since Gyarados is going to Intimidate it, reducing it's effectiveness from the start.
Jolly Flygon @ Life Orb, 252 ATK, -1 ATK, does 34.0% - 40.1% to Gyarados @ Impish nature, 252 HP/252 DEF with Stone Edge. Adamant does 36.5% - 43.1%. Please note that these stats are calculated with both pokemon at level 100, and saying Lance has decided to EV train a flawless, Impish Gyarados.
tl;dr: Jolly Flygon with -1 will sweep Lance.
Flygons most powerful attack against Lance's Dragonites is Draco Meteor, and even then Flygon has to switch out, or Dragon Claw, which is rather pitiful in terms of damage..
Why would you put a special move on a physical pokemon?
No, Draco Meteor is not Flygon's strongest attack, Outrage is.
Starmie can spam Ice Beams, or Blizzard, as well as Surf/Hydro Pump and Thunder/Thunderbolt for risk takers, and recover off the damage, or use Gravity to make sure the powerful yet inaccurate moves hit everytime. A final note is that Modest Starmie is faster than Jolly Flygon, meaning that Starmie is more powerful and faster, and hits Lance harder.
Lol @ Gravity
In a competitive sense, Flygon will be running @ Scarf. Meaning that Starmie is out-sped and hit with U-Turn for super effect and dealing somewhere around 50% (not going to run the numbers).
Lastly, an Adamant Flygon @ Life Orb will still out-speed all of Lance's team, lol. So I'm not really sure why Starmie's speed matters. Also, Jolly Flygon @ Life Orb, 252 ATK, does 82.9% - 97.9% to Impish (lol) Dragonite, 252 HP/252 DEF with Outrage. While Timid Starmie @ Life Orb, 252 SPA, does 83.9% - 99.5% to Careful Dragonite, 252 HP/252 SPD with Ice Beam. Congrats, your super duper x4 Ice-type attack is ~2% stronger than x2 Dragon-type against a Impish Dragonite that no one uses.
"You'll be in major trouble with Lance if that kingdra gets knocked out" should tell you that the OP should consider an ice pokemon (which I should've clarified as something that can use ice attacks effectively) in addition to kingdra.
How? He has Feraligatr, which I'm sure all of you forgot about, can learn Ice Punch.
None of OP's other pokemon have an overwhelming advantage against dragons. Given that all of Lance's pokemon except 1 carry a dragon move, kingdra could be in major trouble, especially since it's not exactly going to outrace everything and knock them all out in one hit. A properly trained starmie with surf/icebeam/thunderbolt could easily sweep through Lance.
See above, lol.
Also, a properly trained anything can easily sweep Lance, lol.
Re-read the original post. "i have a team that needs a dragon because it took me forevcer to beat the eighth badge in HG i had to use my gengar and at least 3 revives."
Got me.
That's a bad set for a competitive Kingdra Ingame it's fine. Dragon pulse so you won't have to deal with the 2 Stage Sp.Atk loss.
Dragon Dance, is rubbish on Kingdra ingame, because of the lack of Physical moves
Other than Waterfall and Outrage, he also has no access to Outrage unless he trades.
He wants to beat his friends also, so I'm giving them the benefit of the doubt and say they are good.
Dragon Dance on Kingdra is not rubbish considering Waterfall and Outrage pretty much hit everything for at least neutral, lolol.
To finaly answer the poor guy's question: Dragonite can be an awesome mixed sweeper, both physical and special, and that's something that Kingdra can only dream about!
We have answered his question.
Also, Kingdra can also me an "awesome mixed sweeper", lol.