Seems like a great idea
I don't understand why this is even controversial.
They're not changing the total paid out to authors (as far as I can tell from the article). Rather they're changing how they allocate the payout.
In a subscription model, there's nothing stopping me as a reader from sampling 20 different books before settling on one I actually want to read. I used to do this all the time with O'Reilly's ebook platform. It makes sense that the authors whose books I actually spend time with should get a greater percentage of my subscription money than the authors whom I look at and then toss.
If you write crappy books with nice covers, then this is bad news, but if you write good books that readers want to keep reading, then you're in line for a pay raise, as the pool of available money is the same, but your cut will be bigger.