I disagree. I suggest you try writing a Windows program that will display the processes running on a system along with the columns of information supported by the process manager.
We wrote various programs to manage processes in a Windows programming course that I took many years ago.
We're really talking about a lot of stuff borrowed from VMS and running through structures and chasing pointers does do real work.
"For example, a simple script that runs a stable set of instructions in a tight loop would load 100% in task manager, but it won't mean the CPU is doing anything useful."
Define "useful". If nothing else, it was stable enough to run 4 cores at a high load factor. Given the fact that it had booted into windows enough to do this, shows a fair amount was working and was stable.