I think I've seen one page override ctrl-f for good reason -- it was a page that lazy loaded literally millions of lines of text that wouldn't have fit into RAM.

Every single other page that does it just wastes my time. It's always a super janky slow implementation that somehow additionally fails to actually search through all the text on the page.

Even in those cases I'd prefer to just be able to natively search the content that has been lazy loaded. I've run into more than one website where the search functionality they bound to control-f is horrible.