For attackers, two moves of the same type are always good because you can use them specifically against Pokémon which are weak to that type.
In Kingdras case that would probably be Dragonite. He is weak to dragon but resists water so your moveset does a better job there. And I think also in general it's better
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i have a 98% IV Kingdra with dragonbreath/outrage. it is better than water gun/ outrage right?
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Kingdra doesn't have a high enough CP to be a good defender or top-end attacker, best you can hope for is a good prestiger.
The two matchups where it could be good for prestiging are against water types using DB/Outrage (you double-resist water, and have unresisted STAB attacks), or against fire types with water gun/hydro pump (you double-resist fire, and have super effective STAB attacks).
The issue is, there are other options for those matchups that might be better. For the first case, grass types only single resist water, but can get super-effective STAB attacks (and solar beam is pretty OP). For the second case, there's plenty of water types with wg/hp that might have a good stat distribution to make up for the single resistance to fire, and there's also Omastar which similar double-resists fire and has the super effective STAB wg/hp combo.
TL;DR : DB/outrage is more likely to useful than wg/outrage, but it may still not be that useful.
Omg you are so lucky, that is the best moveset on a fantastic (!!!) prestiger. The most specific use of your guy will be prestiging against (or just beating) Vaporeon, and lets be honest, they are EVERYWHERE.
Not only does he have a double resistance to Water moves, but he has a very nice attack stats AND DB/Outrage is a fantastic moveset to combine good dodging ability, top notch DPS and a super nice feel to it (DB fast and nimble while 2xOutrage in a row is like being hit by a train from both sides of the track lol).
... I'm envious.
