I had to "Like" the research you did and shared.
Amazon isn't AWS and therefore many efficiencies and accountabilities in AWS (cyber security, benchmarking, billing alerts, logging, audit trails, interaction with ticketing systems, serverless, etc.) doesn't make its way into offers by Amazon.
And the key word is "offers" -- Amazon Business is a Marketing appeal to attract those small business owners that aggressively use Amazon (i.e., first choice before considering vendor or retail option) personally to do the same for their business and who may frankly not have your same concerns due to the few that have access to the business account, etc.
Now I'm curious if Marketing will have a Amazon Business Premier that provides those features you seek.
Thanks again for the list. It's a good lesson to share when speaking to business unit managers about how opting into a SaaS offering doesn't mean the business unit lead isn't even more accountable since the "Shadow IT" behind has not of the support infrastructure that enterprise IT, Finance, and Cyber Risk provides.
All the best, Larry