Amazon sell thousands of things under their own brands that they cherry-picked from their vendors' products and sales data. It is unlikely to matter if your software is open source, it just means making an alternative which they've already done for everything from chairs to Java.

If they're going to compete on $1.28 shower hooks there's no proprietary SaaS with millions in MRR on AWS that will be too hard to copy.

https://www.amazon.com/AmazonBasics/b?node=10112675011