Lets say there is a very successful channel with a total of 20 uploads. Each video is 10 seconds long.
So a person discovers this channel and watches all of the videos all the way through. Thats a total of 200 seconds watch time. Or a little over 3 minutes.
So the new algorithm says "This channel got 3 minutes of watch time"
Now lets take another channel that has 20 or 30 videos. A viewer decides to watch 1 video that is 5 minutes long. The viewer stops watching at the 4 minute mark because the video became boring.
The new algorithm says "This channel got 4 minutes of watch time"
So according to the algorithm, would the 2nd channel be more popular because the watch time was greater? Even though the viewer quit watching because they didnt enjoy the video?