I guess it depends on how you measure "power". By "influence and control lives" metrics, Bezos is more powerful than most medieval kings. Back then, a population of 1-2 millions is quite good for a country with the top ones being around 10-20 millions.

Amazon alone directly employs and provide the livelihood for 1.5millions people. That is comparable to a quite a great king in the Middle Age. Amazon also can influence trade and businesses of countless other merchants and groups in other countries unrelated to these 1.5millions employees by means of blocking access to AWS or removing their products from Amazon. Its reach is global, a feat not many kings and emperors of the past could boast.