Hydro power systems need to store a year or more. Utilities will need at most a few weeks. You don't need or want a river. Dams are f'ing expensive because they need geological support for extreme pressure. An earthen dike suffices if you don't already have a depression.
Only the penstock needs to hold back high pressure.
I'm aware of dams. I'm not aware of your fancy alternatives. It is therefore reasonable to assume that those fancy alternatives aren't widely deployed. And that the main reason for this is that they're more expensive (per energy unit).
Without sources, your (admittedly plausible) qualitative arguments are just a pretty story.
California has constructed dozens of high-altitude, low-head earthen dams on the same principle, over the past century, with penstocks down to lower-altitude turbines, and has lately converted many of them for pumped hydro.
Right now I would bet on a highly unfavourable comparison to be honest. Dams have the overwhelming advantage of letting you build a relatively small wall (compared to the lake you're holding), to hold a gigantic volume of water. The mountain an the river are already there, so you don't need to build them.