> the product owner often works alone and the development team simply receives a stream of backlog items that need to somehow be brought into a cohesive whole This is the root of the problem in my opinion. I am not interested in defending "Scrum", I don't like what I know about it, in the few experiments I've been involved in with it (not by choice), I agree it was disempowering to developers, trying to treat develop…
A "one way" product owner is useless. Backlog grooming is a thing [1]. In fact, I'd say after the Increment, it might be the most important thing. If developers and all the owners are not continually reviewing the items in the backlog together, clarifying them and making sure everybody understands what is being asked for and what the priorities are, breaking down stories that are too big, making sure that, yes, some…
It is not only more efficient, but better for morale to have an agreed upon person upon whom the buck will stop. Sometimes when things are "everyones" responsibility they end up actually having nobody take responsibility for them. Such a person with ultimate responsibility and authority for technical decisions should be both competent and not an asshole, they should be in constant dialog and taking feedback from everyone else, and paying real attention to their concerns about technical matters.
But for the same reason you need a Product Owner (instead of just the amorphous group of all stakeholders) to ultimately take responsibility for decisions about priorities and acceptance criteria, you need a technical lead to ultimately take responsibility for technical decisions.
I think that "Scrum" doesn't have this is just part of it's attempt to commoditize developers (something I think is characteristic of "scrum" but not part "agile" generally or at it's best). "Scrum" sometimes seems as if it's designers thought there _are_ no technical decisions to be made, just a bunch of widget-ized, swappable developers churning out code to meet the requirements set by the PO. But, in fact, there are technical decisions to be made, that will effect other people's work and the product as a whole, in the short- and long-terms. Regularly.