> stemmed from reasons like "they wanted to use some process that I refused to try" or "they made us go through some training that I thought was a waste of time", then I consider that to be a very risky candidate.

I feel like you're gradually making this hypothetical engineer seem more ridiculous. If someone quit over training or their unwillingness to try scrum, that would be bananas of course. There's an extremely large gap between that and mandating the main tool to use to do your job everyday.