I can't address the complexities of the first question/issue.
To the temporary nature of power sources.....I think that is an unfair comparison. Have you spent much time in Lake Powell over the last decade? The temporary nature of that reservior is obvious to me. Compared to coal power plants, as I understand, that system is doomed much sooner. The power capacity of Powell has diminished rapidly since day 1. On the other hand, no one I know would argue that we are running out of coal at the same rate.
And I think that is one of the points of the article.....the framing of energy narratives is antiquated. Labeling hydro, especially like Powell, is simplistic and ignores the reality on the ground. It ignores too many factors to be accurate. The entire renewable vs. unrenewable labels are so contextual as to be useless outside the specific context of each particular project.
I for one believe that there are times that hydro power might be the "best" available option. But I think this article does a good job at highlighting how language and history can get in the way of fully realizing the full costs of such energy production.
And I think your argument of flood control ignores one important aspect....historically, in the western US at least, major populations did not deal with floods the way we have until we built dams. Just look at the issue of Mississippi Basin. As I understand it, populations have moved into areas that would have been problematic in the past under the guise of flood control. Ironically, dams along that entire system have just increased the breadth and depth of flooding downstream.
Maybe it times we abandoned such phrases as flood control .... even the USFS learned how dangerous the word control was in their actions....they no longer talk about controlled burns the way they did in the past.
I won't claim I think some panacea exists in a world without dams. But I think analyzing how our language and historical approaches have led to unpredicted and negative outcomes is the way we move forward to better solutions in the future. If we are not willing to analyze how we frame and describe these issues then we are stuck with the same old choices that are not providing the outcomes we so desperately need. Because I think we all agree we aren't succeeding right now.