The goal of Handmade Hero is to show how to do everything from scratch, not how to make a game as fast as possible using existing technology. I agree that the game is currently light on the gameplay side of things, but he said countless times that he doesn't like gameplay code and that he's an engine programmer. I don't know if you watched a lot of episodes, but actually, each hour of him programming is full of complicated stuff which is hard to follow, but he does that in the blink of an eye. Each time you think that you understood something, he starts doing something way more complicated and he always nails it. Look at how many programming streamers are able to speak 2+ hours continuously without any cut. Most of the youtubers have to look at their source code written before turning the camera on to be able to retype it during the video! Even for a simple Tetris or something!

I'm curious to know what you think is unmaintainable in his codebase. Sure he uses alternative little-known techniques for say, memory management, but once you know what is going on, the code is pretty clear I think.

He posted an issue about the Windows terminal being slow, and proposed simple things to speed things up. What happened? The Windows Terminal team declared that what he proposed is an entire doctoral research project that would be a massive investment. He did the freaking thing in 2 days and said that it's "nothing" and "very simple". The team then apologized for being dumb and is now working on implementing his idea, that they described as "original" and "very valuable"