It is surprisingly close. I download a lot of videos with yt-dlp and have seen ratios where up to 20% of total likes being from Return YouTube Dislike users.

Like here's a video with 188,573 likes in total of which 28,330 were submitted to the data base:

https://returnyoutubedislikeapi.com/votes?videoId=dtjb2OhEQcU

The users disliked 130 times which was extrapolated to 356. No idea how that formula works, I believe users with this plugin could be more likely to dislike videos than users without that plugin which may be factored in.