Why? Almost every website has custom styling and yet it doesn't seem to inhibit users from using them.
Good UI/UX patterns seems to be universal. As consistency is part of good UI/UX there are things that should be consistent with the underlying platform. But consistency with the platform is not equally important for all things. For some things, like window management, it's much more crucial, that it is for other things, like roundness of buttons.
> except in highly specialized software with workflows dependent on prior user experience, such as DAWs
It's not just about prior user experience. If a custom control enhances UX for a specialized task, it has a good reason to break some of the consistency. All specialized software (DAWs, graphics applications, IDEs etc.) have such features. Limiting themselves to just native components would lead to a suboptimal user experience.