Second, relevance and applicability is depending on context. On the context of this discussion, about practical programming in the trenches, what Dijkstra said is irrelevant.
For starters, he was talking about computer science.
Programmers in the trenches (what the thread is discussing) don't do computer science. They merely apply stuff developed by computer scientists (but also by non-scientific practioners in the field), in informal (and often haphazard) manner, to solve business problems (often the same problems again and again, which is something totally beneath a scientist).
So, yes, something Dijkstra had said can still be wrong, regardless of his achievements. And it can also far more easily be irrelevant, as this just needs his saying to be unrelated to the discussion.
Additionally, even if I concede it is an argument solely on authority, just because an argument contains a fallacious point doesn't make it untrue, otherwise that would be the fallacy fallacy.
- Max Planck
Are you saying Max Planck is wrong here? There is plenty of evidence that he was right, that statements made by famous scientists holds fields back because they were reductive or hurting different perspectives. Putting their words at an altar is holding us back.
More like "it doesn't apply" than "it's inherently invaluable"
Also your comment is technically an appeal to authority