The real pain with Waymo is that they just aren't as reliably available in a short period, especially at high demand times. Uber can incentivize bringing on extra drivers at certain times - Waymo can't. Unless they size the fleet for high demand peaks - which would be incredibly cost prohibitive, I don't see how they solve this except maybe a hybrid model or they distill their "waymo driver" into something that runs on a standard economy car.