1000 times this. I want software I'm running to look like the rest of the OS (and every other application) and respect my OS-level UI preferences.
In the case of Win32 using the OS primitive controls mean that your application gets tons of accessibility and preference features "for free" (albeit Microsoft has done a good job in later Windows releases of removing the functionality to set some of these preferences).
There is no value add in making your app UI look bespoke. All the labor you're putting into that work is labor that could be better spent on functionality, features, and optimization. When I see an overly "precious" UI on Windows (owner-drawn controls, animations, fades, etc) I immediately question the ability of the developer to prioritize.