What is the actual issue here? This?
You can’t write data to a 2.0 thumb drive faster than about 50 MB/s. https://superuser.com/a/995350
That is the theoretical maximum; in reality the fastest devices can do about 40 MB/s and if you have something cheap it’s probably more like 20. The speed also tapers off pretty fast as they heat up (although that is more of an issue with 3.0+ devices because they actually move data fast enough to generate some heat).
The metrics you are seeing on whatever tool is announcing the speed of the transaction could be reporting the speed the data is written to cache, then the ugly truth is revealed when the cache operation completes and all that’s left is to wait for that slow, slow USB 2.0 stick to catch up. 