Obviously, reading time is not a perfect judge of quality. Many short writings are of high quality. Perhaps you could count the time spent reading responses also. As they indicate engagement. And that would help quality shorter stories that get good engagement.
I mainly write short pieces, but I welcome the change from the enigma of the previous system. At least, this is method is somewhat understandable. Similar to being paid by the word. A concept writers should understand. If you can produce three short stories in a week compared to one long story, it should somewhat balance out.
We all know attention spans are getting shorter, so long stories are less likely to get read. Which might prevent people from padding their stories to earn more. Time will tell.