1) HR (presumably taking direction from in house counsel) takes the position that it will be difficult to distinguish between a work sample test and an IQ test
2) We are a large organization with very broad roles. The Performance Team hiring for a Senior Software Engineer will probably want a different work sample than the Analytics Team...
Let's not dignify that argument. I absolutely believe you that your company has allowed HR to sabotage your hiring process, and that sucks. But let's not pretend HR is right to do it.
There's probably a solid argument for giving every candidate for the same role the same work sample test; otherwise you might naturally want to randomize some parameters or choose from a bank (if you think "cheating" is likely).
If you or anyone you know is interested I'm a software developer and spend a lot of my time on cloud architectures/containers/multi tenancy optimizations but just generally enjoy solving business problems with technology. In a past life I cofounded a startup that didn't turn out to be viable after going through an incubator (not YC). I have a resume, LinkedIn, Github etc.
Oh, what a terrible tragedy, to give candidates consistent evaluations that are actually comparable between each other... /s
I get the point you're presenting, but at the end of the day it still boils down to "we can't use tests because then we'd have to be held accountable for objectivity, we prefer instead a system that lacks any kind of rigor such that any result may not be effectively challenged, officially or otherwise".