The things you mentioned are not a Reddit problem but an Internet problem. The point of a fediverse is not to avoid the general Internet problems but the centralization problem like Reddit being able to do whatever they want as they control everything.

A few thoughts:

• Unlike reddit, Lemmy provides a way for instances to not tolerate those sorts of activities by limiting what users can join their own instances and blocking entire instances where those activities are coming from.
• With karma not being a public profile stat, there shouldn't be any needs to farm it.
• Without the corporate profit motive and centralized control Lemmy (as a whole) couldn't do what reddit is doing with the APIs. An instance could and an instance could also serve ads, but people are free to move to another instance if they don't like it while still maintaining access to most content.

yes, the problems don't go away but your options to deal with it increase significantly. as of now you are mainly at the behest of the reddit admins with mods doing the bulk of the work but with an extremely limited toolset.

here instance admins are often some of the same people that modded on reddit yet now they operate an instance server with its own blocklists and the ability to filter/control traffic through it as they please (technically possible tooling is going to be ongoing i expect).

there are a lot of similarities to email, your provider or instance will help manage spam and garbage, sometimes things will get through and just like now with your provider youll need to mark some things bad and maybe help dig some of the mistakenly tossed out things in the trash.

there are a lot of ways a "control your experience" discussion can go, since this is a protocol you are free to connect your instance to any other compatible network, there will likely be many in time.

You either die a hero, or live long enough to see yourself become the villain