Being publicly critical of a former employer like this, unless you're talking about major ethical issues, seems like a bad move. There's just no way to do it without it coming across as sour grapes. If you have constructive criticism because you believe in a company and want them to do better, give it directly to the people involved. Otherwise I just have to wonder what the real motive is behind making a public state…
Yet, at the same time I would think twice before working at gitlab now. I feel the CEO or HR should have had an NDA in place with a generous severance. Also, I would be hesitant about hiring the engineer. He was given a great challenge, but instead of rising to it, he made up excuses about needing mentorship. At the very least, he could've generalized the problem, and made an open source library as leverage for findi…
It sounds like he worked his butt off, what more do you expect? I don't scale mountains for my employer, I do what is reasonably asked of me - and it sounds like he did just that. Sounds like a typical chaotic startup culture growing too fast for its own good, not paying attention or supporting its employees' needs.