And they're both lazy writing.
Ki is just "inner energy my characters can shape themselves" while Nen/Chakra is "Ki I can make do anything my plot requires".
It's all just poorly defined magic shit, or defined magic shit that the writer ignores anyway whenever he needs it to.
That's how all shounen anime is.
1. Introduce mystical energy.
2. Explain rules for mystical energy.
3. Introduce characters that ignore those rules. Call them "special".
I actually think you were right the first time.
Gon and Naruto are both typical shounen protagonists. But Sasuke is a lot more like Kurapica than he is like Killua.
I mean Sasuke/Kurapica is literally two character obsessed with obtaining power so they can avenge the slaughter of their clans. Also magic eyes.
Sasuke is just Kurapica if you take away Kurapica's redeeming qualities.
Killua may have the whole "comes from an elite family" thing in common with Sasuke, but their personalities couldn't be more different. Killua is geniunely friendly with his rival, he has a playful personality, and his driving motivation isn't vengeance, it's freedom.