I think the current status quo for databases is canned software. And this isn't necessarily bad because neither of the three databases mentioned hide their specs or default settings, the three have very good docs and community willing to help, in addition to companies giving commercial support. Whats your excuse to misuse these products?
RethinkDB writes your data to disk before acknowledging the write but on the other hand can't elect a new primary in case of failure, two completely different features/limitations that might work for someone and not for other ones. Is that hard to understand? Did mongo documentation lie you at some point?
Accept that you are "buying" a general purpose product, the designers thought that their users will need those features, deal with it.
Otherwise build your own database, I know this might sound very hard but I guess in the future we will see smaller building blocks that let you build something that handle your needs like this: