So yeah, feel free to disagree with Uncle Bob, but in no way is he "under-substantiated.
Am I allowed the opinion that it was bad for the industry, and some of the ideas it integrated are harmful and still holding us back as an industry?
It's convenient that we have no crystal ball into a parallel universe where agile never became popular.
Part of how you feel about agile likely has to do with the industry you are in. If you're doing embedded systems for cars or medical devices, agile is absolutely trash. But for the very large world of consumer facing software, or even business software that isn't dealing with life-or-death situations, the agile world is so much better than the waterfall world.
Instead it was a bunch of vague maxims, that became a cult collection of heuristics (nominally rooted in Java, as much as it claimed to be polyglot).
The counter-argument to this is "No True Agiles-man", so the brand never needs to take responsibility for the reality, and this defense is as much a part of the culture as anything. It's like agile is a religion, and the manifesto is the religious texts - selectively ignored or interpreted as needed. No, I don't feel this is much better than waterfall, especially as even that could have evolved into more user engagement, without the mantras ("waterfall is bad" itself being a mantra) - why can't waterfall be a "tool in the belt", or a reasoned stage in the process? Why can't agile principles be taken individually rather than adamant on the whole? Why can't sometimes people be more important that process, and sometimes process more important than people? Why can't we have a plan (moreso upfront), and still respond to change?
I don't know, I think we did: what is called "agile" today is all of the exact same stuff that the agile manifesto was explicitly the opposite of. Agile became popular among developers, managers didn't really understand what it was, consultants rebranded it to be exactly what it was supposed to be a replacement for, managers were happy, and developers went back to being frustrated.
I wish we could bring ourselves to value writing code that is accessible instead of conjuring up gibberish that reads like a pretentious scientific journal. Uncle Bob has literally been saying that we should write code that anyone can understand easily. Hardly a radical elitist concept.