Nah, it's not redundant just yet. For starters the components provide a basic sort of 'design' for people who suck at designing UIs, like myself. For them, it means they've got a decent default style for things like buttons, burger menus, slideshows, alerts, etc. That's still useful to have, especially if you can't afford a designer.

It's also still very good for quickly mocking up user interfaces, especially ones for boring stuff like admin panels where you don't want to be stuck focusing on the UI rather than the actual functionality.

Finally, it provides a nice sort of built in style guide for a project you're not used to yet. If a site uses Bootstrap, well you know immediately what classes you need to use for components, what blocks of HTML are needed where, etc, and you can much more easily teach that to a new developer too.

So while its usage for grids is certainly on the decline, it's not dead just yet.