I think we can agree to disagree on which is worse.
The next president is making a bunch of public actions that will be critiqued, audited, and probably checked / balanced as the government was set up to do. The CEO of reddit is SECRETLY tampering / modifying the "speech" and content of private citizens without any checks, balances, or even repercussions (so far).
I'd also argue that reddit has a more direct engagement model with private citizens that makes this hit closer to home (i.e. if we actually were real-life friends, or internet buddies for years, and one of our messages/comments to each other was modified that could cause far more direct impact — e.g. "you" convince me to commit a crime because you have my trust as a "personal" friend)
I'm honestly surprised he publicly admitted to it at all, and I'd further be shocked if he doesn't end up stepping down because of this incident.