Yeah, there's some truth to both your points. If you need to backfill someone for an existing production project that doesn't have the bandwidth to train them effectively you are setting that person up to fail. This is why tech interviewing is such a pain in the ass though as there are a lot of competent programmers who can pick up new languages quickly. When we decide on who to hire while at megacorp it is always - generalist or specialist. When we decided on who to hire while at a start up it was always - growth minded and quick learner.