"Not having the time" to introduce new engineers to the problem at hand, task, system or what ever is a recipe for wasting even more time in the future. It's very short sighted. Neither "10x programmers" or mere mortals can grasp a code base by reading it alone as by a thorough introduction.

I mean, a mediocre engineer that knows the system well is way more useful than an excellent engineers that just got his hands on it, for like half a year or more depending on complexity. If you give guidance you don't need excellent engineers. At least not as many. It's kinda surprising the way companies think of this.

Rather than officially allocating a developers time for introducing new employees or writing documentation for the system, Company 101 is to put 10 or 100 times the amount of dev time into catching up for the devs replacement when he quits, after he quits.