I think it’s different for developers

Oh this is such a hard path to tread, and again the same time hard to know without hindsight what the right path is. I come across lots of situations, with legitimately bright developers, who have replaced a standard subsystem either a home-grown one, usually for performance reasons. In that moment in time, in that context, the general solution was less performant or had an ugly bug, or whatever, so they replaced it with something designed for the one specific context. But then the context changed, and now heres this bastard-child that's been narrowly designed, and optimised for performance (so hard to maintain or change. ). And the developer is somwhere else. But equally I've spent a career writing the "new standard solution", which of course started out as an alternative to "the standard solution". And in our context that -has- made a huge difference. So it eould by hypocritical if me …

For several bosses, this scenario you describe has fallen under the concept of 'kill your heroes'. Sometimes the person really is brilliant and you should do anything to keep them. But if it's because they're the only one who understands their code, then they are a liability.