The thirty second impact will be negatively huge for some stories. I can skim a lot more than 500 words in thirty seconds.
But it may well be positive for others.
Are those stories we skim really worth much? If we haven’t found value in 30 seconds, do they matter?
Giving them little or no money increases the pot for the stories that do have value. It remains to be seen if that will cause writers to write longer posts. But that may be counter productive; I often abandon stories that drone on and on and neither clap nor comment when I do.
So it may well increase earnings for the stories we actually read and engage with. That’s as it should be, isn’t it?