My 2 cents: Let publications set the payout ratio they prefer. Let Medium handle the payout logistics.
Publications can “compete” for the best writers by increasing the payout ratio in increments of 10, starting with the default 50:50 and opting to bump it up to, say, 70:30 in favor of the writer.
More established pubs may position themselves as prestigious and exclusive, and keep a majority of the proceeds.
Let the free market rule!