Kleptomancy ruins an important balance aspect: income rate

Before you downvote, consider this: for it to benefit a champion more than any other keystone option, it by its nature must be overpowered.

Why would a champion take Electrocute, Arcane Comet, or Press the Attack? The answer is pretty obvious-- to have more damage, because more damage means more kills, more kills means more gold, more gold means you get stronger more quickly than the opponent and can win the game earlier, when having that lead matters most.

And in general those who take damage keystones are the champions with relatively strong early damage, the ones who are rewarded for being aggressive earlier.

Now, why would you take Kleptomancy? There are three reasons which must be met for it to be your best choice:

• You scale well with items-- making you a late-game champion.
• Your early damage is so weak that bringing a damage keystone wouldn't supplement it enough to reliably get you early kills, especially against an early-game champion with a similar damage rune.
• You are not an on-hit/sustained damage champion. Because though they do also scale with items, they're better off bringing either Lethal Tempo-- to amplify their strength once they're around half build and beyond, or Fleet Footwork-- to help them survive the early game and kite with more ease come time for teamfights. Or for non-marksmen, Conqeuror since it provides a similar damage boost to tempo.

So you're best off biding your time and playing safely until you have items, mainly from farming. As a caveat, your power spike doesn't come until far later in a match. That's how it's balanced out. In exchange for the risk you could lose early if you aren't cautious enough, you get a better chance at winning as the game gets further along.

But Kleptomancy allows you to bypass the very aspect of your playstyle that makes it balanced-- the over-time nature of income. It's perfectly fine to get a reward for reaching 4-6 items when the enemy has had ample opportunity to capitalize on your weakness. But Kleptomancy brings you to that point much sooner than you're supposed to be there.

Subsequently, if they're to keep Kleptomancy in the game then you have to be nerfed to compensate (as with Gangplank), or held back from needed adjustments because you reach late game items far sooner than the actual late game (as with Ezreal). Which is very, very odd...

Because outside of the recently-removed cheese strat of abusing support items at top, Gangplank and Ezreal are the only champions it's been the best option for. (You might count Illaoi, but as of the introduction of Conqeuror it's been outperforming Klepto on her by quite a lot). So that's only 2, maybe 3 out of 143 champions who are best off with this rune. In my opinion, far from enough to justify its existence.

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I think it should be removed from the game, and replaced with a different rune suitable for the Inspiration tree but unrelated to income. Perhaps something to do with experience. Maybe something like, if you're in the proximity of an ally who doesn't also have this rune, you gain full experience from minions they kill. Supports could bring it to hit two and six a level sooner and partially supplement their lack of income with levels.