It was always the wild west. Windows was full of "native" apps that reinvented their own UI. Off the top of my head:

- Office (custom widget toolkit, menus, toolbars, etc)

- Internet Explorer (frequently introduced new toolbar designs not available to apps via API until later)

- Encarta (custom dark mode-ish theme)

- Netscape Communicator (custom toolbars)

- RealPlayer

- QuickTime

- MSN Messenger (custom theme)

- Every video game ever

... UI inconsistency didn't arrive with the web. Even macOS has always been a patchwork. Apple couldn't stop introducing new themes over time and there were always apps that didn't quite follow. Brushed metal!