Right on the money with the "Real World" anecdote.
We do penetration tests for a wide range of clients across many industries. I would say that the bigger the company, the more childish flaws we find. For sure the complexity, scale, and multiple systems do not help towards having a good security posture , but never assume that because you are auditing a SWIFT backend you will not find anything that can lead to direct compromise.
Maybe not surprisingly, most startups that we work with have a better security posture than F500 companies. They tend to use the latest frameworks that do a good job of protecting against the standard issues, and their relatively small attack landscape doesn't leave you with much to play.
Of course there are exceptions.