and without GPUs, mind you. And a lot of that trickery probably came down to: let's write everything in assembly. Fruity Loops was absurdly fast in the early 2000s and was written in Delphi and assembly, IIRC.

In 2023 DAWs should not be that difficult to make fast. It's a solved problem. Multi-channel audio processing is one thing that modern CPUs should not even break a sweat at. I believe this article has uncovered the basics that have made every DAW complex from the beginning, but seems to be focused on efficiency with your bog standard off-the-shell GUI library. That's the mistake, IMO. None of the DAWs I know of use, for example, standard GTK. Even the ones that do use a GUI toolkit use it minimally, for the file pickers and configuration. Not as the primary interface for the DAW itself. You need to go lower level and remove the layers of cruft. I mean hell, adding language bindings on top of everything is going to add yet another layer of inefficiency.