Pangram specifically (as opposed to most other detectors) publish internal audits, and seem to welcome external audits [0]. I'm not saying that you are necessarily wrong, just that in my opinion they have earned a higher bar of criticism than random one off anecdote.
That's a fair criticism, I certainly didn't run a full benchmark. Just a few of my own pieces of writing. I also did it a few months ago, maybe it's gotten better since.