All of these companies can pay either as much as Google or more than Google to attract the topmost talent pool. In fact, many of the engineers in these companies frequently hop from one company to another between these. Of these, Amazon has the highest attrition rate due to stressful working conditions and they are sooner to leave to another company than the others.
Walmart Labs in Bangalore has a talent pool that is running a million node cluster based on OpenStack completely in house with zero dependency on something like AWS (of course!) or GCP. That's quite a feat and I think it will help Flipkart a great deal if Walmart Labs shares some of this incredible talent and resources they have built within their company.
Disclaimer: I work for Flipkart.