Writing a script has always been simpler than making a proper installer, because you need to adhere to various transactional rules, implement a proper rollback mechanism, worry about making your components have correct keys that still work after an upgrade. And e.g. if you need to install a Windows service, most of the standard options (even those provided by Wix) don't cover all cases out of the box. So to some extent using a script means replacing a more complex, but complete solution with an ad-hoc thing that may work in general, but fails a lot of corner cases.

What has changed since these days of Microsoft? I’m pretty sure when it came to setting up complicated systems, you had to follow a 158 pages document with all dialogs you had to click to (if you’re lucky enough to have a document like this)

In this sense a predictable powershell script is IMO an improvement

Haha, I might have written almost the same thing but late by 2 minutes :)