Well then ask yourself who’s doing the manipulation? The instance owner? The open source devs who make the engagement algo?
The open source devs are going to be in line with keeping it transparent and healthy while still keeping it entertaining, so there’s already checks and balances right there to prevent it becoming an issue. There is no venture capitalists to corrupt it either, so there’s no incentive to make it malicious and the community gets to tweak it to make it balanced. That also means anyone can check to see how it works. Also they can add options for the user to tweak it.
If you don’t like it, then the current option of new posts/boosts in order will always be enabled, so this would be a completely optional separate feed and not affect you if you don’t like it. No need to police others and decide they don’t deserve to have this implemented as an optional sort, and it’s not replacing your current feed.
If a instance somehow maliciously manipulates the algo, then that’s the beauty of decentralization right there, you’re free to swap. The problem with other social media algos is they’re corrupted by venture capitalist and they’re centralized so you have no say in how it works. Both these issues don’t apply to Mastodon.