Echo = hub, too expensive and large to buy 10 for every room in the house, used for receiving, processing, routing info from spokes and cloud
Echo dot = spoke, microphone and AI functionality at a lower price point, distributes connectivity network throughout the entire house so that you don't have to walk from your kitchen to your living room to order new paper towels from Amazon
not hub/spoke at all. the dot and the echo are separate standalone products. The only reason you're required to own an Echo to get a Dot is because it's a "limited supply" product, and they want to make sure that only loyal customers get to review the new thing in order to seed some positive reviews.
Echo = hub, too expensive and large to buy 10 for every room in the house, used for receiving, processing, routing info from spokes and cloud
Echo dot = spoke, microphone and AI functionality at a lower price point, distributes connectivity network throughout the entire house so that you don't have to walk from your kitchen to your living room to order new paper towels from Amazon