The old mac minis used to throttle (temps up to 90 degrees). There isn't enough cooling in these tiny machines. It's basic engineering. The iMac Pro has far more advanced cooling and that has throttling issues. Apple just need to add an AIO cooler and it would solve these issues but they prefer to have quiet fans instead so the design isn't compromised.Prove it will throttle. Point me to a review that shows it throttling.
https://appleinsider.com/articles/17/12/29/video-does-the-imac-pro-get-too-hot-when-under-load (read the last paragraph)
https://discussions.apple.com/thread/7068280