Amazon growth has been predicated on cannibalizing other companies since 1995. Bezos was very specific about that in the business plan he presented to investors: he wanted to own all of retail, and has largely succeeded in that.

From a valuation perspective, what's so wrong about that? You want to be on the side taking over the world. Otherwise you're on the side that's getting taken over, and the value of your equity logically trends toward zero.