I had a similar experience working for a company that had, essentially, developed their own in-house web templating language and programming system. They'd started before PHP or any of the other server-side programming languages had caught on, and while a decision to use a homebrew system may have been justifiable in the '90s, when the only real alternative was Perl/Mason, by the time I joined (2009), it was long overdue for them to have moved on to an industry-standard solution. PHP. Python/Django. Ruby/Rails. Even classic ASP would have been preferable to the mess of C++ and XML they were using.

Frankly, I think the article, like a lot of Joel Spolsky's writing, has aged like milk. For example:

    If you’re developing a computer game where the plot is your competitive
    advantage, it’s OK to use a third party 3D library. But if cool 3D effects
    are going to be your distinguishing feature, you had better roll your own.

Except, if you look at modern games, even ones with very high performance effects, that's not what they do. They use one of a rather small number of 3D engines, like Unreal or Frostbite. It turns out that developing cool 3D effects is far easier if you have a battle-tested performance optimized framework helping you. CD Projeckt Red abandoned its own in-house engine (REDengine) in favor Unreal 5 for future development, in no small part due to the issues that they ran into trying to extend that engine for a massive open-world game like Cyberpunk 2077.