❔ Why is the data usage inequal for the same amount of tasks from different providers ?

Could be a variety of reason such as the actual request etc. are different on each request a bot will send etc. The way Oxylabs and other providers work is that we don't have access to the proxies directly and we don't have anything in the middle as the usage is directly from Oxylabs API not from our API. The data on your account for example, every time you go to the dash and click view usage it calls Oxylabs API directly and displays the data usage.
It's like for example when you test like 10 proxies once and you test the same proxies right after that the speed of the same proxies will be different.