I have a CS friend who just recently got hired for walmart (not sure on terminology, but he does some analytics stuff). Your account sounds pretty accurate to what he described, but add in a dollop of basically every technology that's ever existed and was ever popular at any point. He's been there a short time and already had to look into systems running on cobol, hadoop, oracle database, SQL Server, MySQL, Firebase, C, C++... Pretty much they hire contractors to implement any new project, and then hire H1-Bs to maintain it afterwards. He said his job is mostly managing H1-Bs, rather than actually writing code.