“Essentially, the Culture must have value lock-in for the values of the Minds that were present at its founding.”
Probably at least some value lock-in is somewhat required, unless you want the particular civilization to fracture. If it is allowed to create your own cult of space nazis intent on exterminating everyone else, your post scarcity utopia may not live long. Even “live and let live” is a value, and many people do not subscribe to it.
“But I think it is more likely that it was achieved by genetic changes, so that it’s safe to raise full Culture citizens in other cultures”
I agree, or at least that genetic change is also a strong contributor. However, if you think about sociopathy as a disability that in most cases makes one’s and their fellows life worse, this genetic modification is a good thing.
“In other words, these superhuman minds have not solved alignment”
I think they did kinda solve it, as long as the other system is somewhat dumber than they are. Just as we are able to more-or-less align dumb systems, probably Minds can do that too. As long as they are not another mind or comparable level.
I think it really is a somewhat large disempowerment to humanity, but I see this as a better alternative. It might sound great to make all the important decisions, but in the end, humans are just too limited and we would likely fail and ruin ourselves. A Culture where humans make the final decision could not have won the Idiran War. If I am to play chess against Kasparov and my life depends on it, I would much rather let Stockfish make the decisions.
I am pretty sure there are honest and well-meaning financial advisors too. E.g. there are valid and professional blogs/youtube channels (e.g. “The Plain Bagel”). There are some confounding factors though, in particular, pretty much anyone can call himself a financial advisor. Even if they do not know anything about finance and their only goal is to sell overpriced insurance policies.