Some times the problem isn't one piece of code that can be solved by adding an if-statement somewhere, some times it's the whole architecture of the module and the only way to solve that is to rip the whole thing out and replace it with something new. Reviewing such a "change" (it's more of a new feature actually) does require you to understand it completely and not just within the context of an insertion between two other lines of code. Being too scared to do such a replacement can easily lead to stagnation and fire-extinguishing that never solves the root cause of a problem.

It's 17 commits, each that do one thing.

even Quicksort got faster if you check for runs i.e. already sorted parts. More code but faster.