I think rimu has made the karma system to be optional (i.e. in the admin settings, not hardcoded) so we'd just disable it anyway. I think the second feature should only apply to mods/admins, since its a very useful tool. #1 #3 i agree, they are not good.
I'll address each point in the Piefed Features for growing healthy communities:
Find people who have low karma
This applies to admins, and while not really that effective, its okay to have.
Find people who downvote too much
This is a very useful tool, since this is a big problem on lemmy. Same thing; only for admins
Spot spam easily
Sounds like a good idea; but with feature #3 as you pointed out, this might cause some new-user shitposters to get falsely flagged, but we would disable it anyway.
Don’t award karma in low-quality communities
This is now opt-in, and we would disable it.
https://chat.piefed.social/#narrow/channel/5-admins/topic/Low.20reputation.20communities/near/1872
Warnings on unusual communities
We would add nothing to communities, anyway; users are free to do whatever they want, themselves. (maybe to our own instance communities like /0 and governance? But not much honestly.
Icons next to comments by low karma accounts
As i said before, probably should only be seen by admins/mods.
Icon for new accounts
No problem here; most clients do this anyway.
Automatically delete content based on phrases in user name
Sounds very useful, and which is why piefed didn't struggle at all with nicole.
Report accounts, not just posts
Good idea.
Instance-wide domain block
We have this on lemmy too
Automatic reporting of 4chan content
Not a good idea imo. We'd disable it.
Plus it's written in Python and has only 1,6k MAUs, so we can only guess how well it scales
We'll always have this lemmy instance anyway :) but afaik it scales fine, and has some optimizations coming along soon.