Youtube always kept downvotes and the 'dislike' button, the change (which still applies today) was that they stopped displaying the downvote count to users - the button never went away though.
Visit a youtube video today, you can still upvote and downvote with the exact same thumbs up or down, the site however only displays to you the count of upvotes. The channel owners/admins can still see the downvote count and the downvotes presumably still inform YouTube's algorithms.
I think that just the absence in official app and the existence of this tool makes this point largely irrelevant. Company in question could easily reverse this decision overnight as the data exist, but absent that people adjust to an available proxy estimate. It is interesting though, because it shows clear intent of "we don't want to show actual sentiment".
The official youtube stats (views, comments, upvotes) are not real/real-time either. But that's the best we have. And dislike numbers are in the same universe of credibility and closeness to reality. It's definitely good enough.
If you want downvote data be more precise, do your part and install the extension! :-)
Visit a youtube video today, you can still upvote and downvote with the exact same thumbs up or down, the site however only displays to you the count of upvotes. The channel owners/admins can still see the downvote count and the downvotes presumably still inform YouTube's algorithms.