> It feels like that particular research direction is now a dead end

This is the most negative possible take on the most positive possible kind of result in CS.

To see just how unduly negative it is, imagine how different your response would have been had the exact same result been reported in a paper by exclusively human authors. Would you have likewise accused them of creating a research "dead end"?

EDIT: Changed "by, e.g., Ryan Williams" to "by exclusively human authors". Without having checked the authors, who include Ryan's wife and frequent collaborator Virginia, I had reached for a big name in the field purely as an example of a human who might well have made this breakthrough on their own.