It seems like the main benefit of such frontends is the lack of trackers and fingerprinting, but what if the browser, like Firefox, already did that with UBlock Origin and fingerprinting protection?
That’s not entirely correct, invidious doesn’t act as a proxy. From the invidious faq:
By default, the video stream is fetched directly from Google’s servers (
googlevideo.com
) in order to reduce the bandwidth required by invidious, meaning that Google will be able to see your IP address and some other data commonly sent by web browsers, like your user-agent string.