What if Pyke didn't share kill gold with his allies?
This would give him the same weakness that every other assassin has: he'd funnel too many resources to himself, and would thus put his own team behind. It's the reason why it's bad for your team if you for example go 30/0 on Fizz: yes, you can one-shoot anyone in the enemy team, but then while you wait for your cooldowns the fight becomes a 4v4 between the enemy and your own kill-gold-starved team.
This though would also make him more hated than he currently is, but it's not like there's no other champion with a resetting execute that tends to multi-killsteal (
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