I partly disagree with you on this approach.

Dealing with abuses is one part of the balance. And I might be wrong, but I believe flag wars are only a fraction of abuses. I agree when there is no retaliation there's nothing from stopping the abuser from reaching higher highs. But retaliation brings in a matching retaliation (in time). I don't think many non-combative individuals will want to join a platform consumed by ever growing flag wars.

Do a full history reputation rollback on the entire blockchain

I doubt anyone would dare to try something like this. Many well-established steemians use or used at some point bidbots. I haven't, but I think this would provoke a major mutiny.

UA also comes with its own false curation

I also think @steem-ua gathered an important traction. It can and should be improved (and I'm thinking here about UA too). I think you are right about the false curation. But when true following and engagement is missing, what else is there?

Have @r0nd0n and his people moderate the flag queue. If they mark the flag, the UA service tries to cancel or attenuate the flag.

Give @freezepeach the voting strength of the UA service to use when needed.

I disagree that @steem-ua can be put in the service of @freezepeach. They have different roles, and most likely, support.

Replace the algorithmic curation with an algorithmic vote follow. That is, don't upvote posts of delegators based on the UA of the delegator, upvote posts upvoted by and downvote posts downvoted by the delegators based on the delegator's UA score instead.

I don't think it's possible, although it is an interesting idea. No single project would have enough SP to give significant votes in these conditions. Some bigger accounts (and even smaller ones) might cast a lot of votes per day at lower weights. The other issue is incentive to delegatators disappears or diminishes, and some are looking for it.