Tony Xu, co-founder and CEO of DoorDash Inc., smiles during the Wall Street Journal Tech Live conference in Laguna Beach, California, on Oct. 22, 2019.Martina Albertazzi | Bloomberg | Getty ImagesDuring the depths of the Covid pandemic, with restaurants around the country facing an existential crisis, DoorDash CEO Tony Xu had an unconventional proposal. He wanted to cut commissions.Chief Business Officer Keith Yandell worried that such a move would result in a massive hit to profits ahead of the...