Well, I tend to spend a lot of my spare time noodling on what I think of as fundamental CS problems (what's the optimum radix for a min-heap? 3, I think, not 2), and I've spent a fair amount of time programming in languages like C where implementing mergesort from scratch is actually a practical thing to do. And I have a prejudice in favor of knowledge with a significant shelf life, like how mergesort works, rather than, say, how to work around the bugs in the latest version of React, which is also practically necessary for getting stuff done. So I might have a bias in favor of that kind of thing.

I certainly agree that mergesort is a lot harder than fizzbuzz, more than an order of magnitude. Fizzbuzz is well under a minute.

I'm pleased that you enjoyed my comment and code! I was reluctant to make it because I feared you might interpret it as an attack.