Well, there's also "I've been here 2 years and it's obvious to everyone that I'm still struggling" and "I think I've become so demoralised and feel so marginali

Well, there's also "I've been here 2 years and it's obvious to everyone that I'm still struggling" and "I think I've become so demoralised and feel so marginalised that I've lost a lot of the fire..." So this dev knows he's been struggling and he knows everyone around him knows it. There's no indication at all that this was a surprise to him or that the problems hadn't been mentioned earlier. It sounds to me that the manager gave him much more time than was really deserved to catch on, and he simply never did. We're both guessing a bit based on incomplete info, but it looks like the message didn't go from "you're doing great" to "you're doing horribly", but rather went from "you're struggling but we're willing to give you time" to "you know, time is almost up". If after two years it's obvious to everyone that you're the weak link, then while training might help a little, you're probably just in the wrong place.