Unpopular opinion: optimising for "branding" is what killed theming. Everyone wants to have their own custom colour theme, brand-associated font or button style, which clashes with uniformity of system controls. If everyone renders buttons in a custom way, they bypass the native, theming-capable, accessible-by-default system controls. As long as product managers are happy, it doesn't matter that users aren't.
If an app can't survive on its usefulness alone, it probably shouldn't exist.
As a user, if an app doesn't have a native UI, I disregard it unless I need it for a specific and mandatory use.