Creating an alternative form of communicating appreciation that has no impact on algorithms is your strongest and best argument.
Initially, I was resistant to your idea for a Thank You button, but this sentence changed my mind.
John Ward

Given that you - Chris Messina – just highlighted this, don’t you think it’s an even better implementation of what you’re suggesting.

This highlight didn’t alter an algorithm. It has a level of anonymity as it doesn’t show who it’s from until you tap on it. It shows your appreciation precisely better than a general thanks.