What would be really informative would be to see how the same relative message would be transformed from an email to a push notification. It makes sense that push notifications are more effective, even in the lower range, but do they really include the same content as email? Yes, you might get an email about a gift card tier you qualified for and that can be a push notification. What about emails for sales going on? I think those would not work as push notifications, so this could be skewing the numbers. It could be more emails get sent out then push notifications.
Everyone talks about omnichannel marketing. I think what's often forgotten is that you don't just send the same message across all your channels. You have to find that right channel for the right message. Those retailers that are dependent on email for everything are going to lose out on those that aren't.