Dams still get built for non-power reasons, to manage water supplies, so adding turbines (and floating solar PV) to them might make sense, but yes I think we're now at the point where new hydro purely for energy production is going to struggle to make a case for itself against just deploying renewables and batteries and interconnects.

edit: to add some context re the Hoover dam:

> Upon becoming Secretary of Commerce in 1921, Hoover proposed the construction of a dam on the Colorado River. In addition to flood control and irrigation, it would provide a dependable supply of water for Los Angeles and Southern California.