They way they approached their job at Amazon using git blame, finding out who to ask for help, and debugging, are all great signals to me. Conversely, a junior/mid who doesn't ask for help is a massive red flag to me because it means they're either struggling silently or probably going down the wrong path. I've worked with people who spent weeks working on the wrong solution, way worse than a two hour pair programming session when they initially got stuck.

After only two years in the industry they sound on par with where they should have been. Thinking too much into where you should be at can definitely set off imposter syndrome. For my first 3 or 4 years I was blissfully ignorant, I really didn't have a good understanding of what I was doing; I just made things work in whatever way I could. When I think back on those times it blows my mind that I used to be able to confidently hop into new codebases with new languages and write code. Today I dare not touch anything until I completely understand it first. Sometimes this can be crippling.

It sounds like this person was in the wrong environment which probably didn't help the mental issues that ensued. But I wouldn't put any of it down to being a bad software developer.

I'm sorry for their situation but I'm glad they were able to get help. Perhaps one day they may change their mind and get back on the tools.