kingdra vs dragonite

I would advise no and keep it as is as to prestige against Dragons. Since Horsea candies are common you could hunt around for another high IV one to obtain DB/O ( or by the time you obtain a dragon scale again you might have a great horses or seadra) that might be worth powering up....

Yeah I think DB/Blizz Kingdra is a bit of a dud. At it's very best (aka against a Dragon) it's not as strong as a DB/O Kingdra which also has awesome matchups against fire and water (Vape). Blizz is resisted by fire and water.

My 98 Kingdra got DB/HP which is also a bit of a dud in that either WG/HP or DB/O are nearly always better, if not always. DB/O is what most people will wish for because of Vaporeon and to a lesser extent Dragonite (because King still takes SE dmg from Nites dragon moves which usually means a roasting).

Technically his ultimate matchup is when he has WG/HP and he fights a fire mon with fire moves. In that case he deals SE STAB dmg and dmg against him is double resisted. The downside is that fire mons don't feature that heavily in gyms anymore (in my experience) compared to Vaporeon.

The difference between Blizzard and outrage vs dragonite is not that big, yes Outrage gets STAB+SE, but Blizzard gets 2x SE vs dragonite. Having said that, you are gonna have to be very good at dodging, because you are also getting SE damage from dragon type attacks, and even if the defender has Steel wing you are still taking quite a bit of damage. Kingdra's best matchups are vs water and fire pokemon, given that you have water attacks vs fire or dragon attacks vs water, still you could use him to prestiege vs dragonite, as a lvl 30 Kingdra's CP ranges 2K, where a lvl 30 dragonite ranges 3K.... as long as you dodge... a lot.