Honestly I'm a bigger fan of Kingdra GX than Dragonite GX
Dragonite GX requires mixed energy pools, and decks that roll two inventories of basic energy are inherently less consistent than single energy decks. This would also be a DCE deck as well which makes that energy pool even more awkward. Weakness to Fairy is terrible since there are lots of great Dragon Pokemon coming out, meaning Gardy/Sylveon is going to just get free autowins. You might be able to turbo out Dragonite GXs thanks to Lance Prism Star and Zinnia, but that occupies your supporter per turn which you might need for Guzma or Cynthia instead.
Kingdra GX hits for 190 choice banded on just 3 energy, same as Alolan Ninetales GX or Raichu GX but with no side effect, which covers every basic GX that matters right now. Being a one energy attacker means that it can just swing for 60/90 and follow up with 2 hit KOs next turn on 110/140. It's a slower set up, but it gains momentum as opposed to loses it over time. Weakness to Grass is alright since Golisopod GX and Decidueye GX aren't exactly killing it in the meta ratios, nor do I see them making a crazy comeback post rotation (I could be wrong). Post rotation, I really don't think being a Stage 2 deck just means you're going to lose. Basic GXs lose Max Elixir and everyone loses Sycamore which slows down the game a LOT, and the fact that FFB is leaving the format means that the HP values that a Stage 2 offers actually kind of matter now. 230 is hard to hit for most Basics and Stage 1s.
I dunno. Not that I dislike Dragonite GX by any means, but the more dragon stuff comes out the more Gardy is just going to autowin while Kingdra GX has no fantastic direct counter at the moment. But I guess that's why Stakataka GX is coming out to complete the weakness triangle a bit.