As though mistakes wouldn’t happen with non-programmers working in R.

In R, you can use accepted methods of software development and engineering, such as version control, automated testing, CI/CD to catch mistakes and prevent them from causing harm. In Excel? Not really.

Do you think the average finance department employee is going to do that?

Especially those departments should do so and learn to do it. Financial departments are always the ones complaining about the cost of mistakes, compliance risks (of the monetary kind) and doing due diligence. Preventing the production of wrong figures in financial excel sheets ticks all those boxes. They should bloody well be doing it, but I'm also not holding my breath ;)

And there are massive bugs in programs that use these tools like the Linux kernel still.