One thing about junior devs is the level of skill varies greatly. Where I work there's a guy who is nominally a junior dev, but he already knows everything the senior devs are expected to do. If he was an average guy there'd be a lot more handholding, but somehow with barely any hiring process (he was a friend of a friend) we lucked out. I'm wondering whether management will be smart and pay him like a senior dev so he doesn't leave as soon as he finds out he could be making a few hundred grand instead of a few tens.

One major downside of this kind of variation is managers think they can somehow repeat the trick. If we just make the hiring process hard enough and shove enough candidates through, we can pan for those elusive 10x guys. It also makes people think that 10x guys are a thing like a gold nugget in the river, rather than the outcome of a long process of maturation in an appropriate environment.