You might enjoy the alternative approach taken by .NET's threadpool which uses hill climbing to dynamically adjust the number of threads. See this articles [1] and its references to Microsoft's papers on their design. Semi-relatedly, I used hill climbing to adjust the eviction policy in Caffeine (Java cache) to favor recency/frequency. While it seemed simple and naive, it worked surprisingly well and robustly.

[1] https://mattwarren.org/2017/04/13/The-CLR-Thread-Pool-Thread...