windows 8.1 is not better or worst than windows 7, it is more updated with security form Microsoft updates , and in some cases windows 8,.1 will run better than windows 7 on certain type of hardware that do not have drivers for windows 7 to full optimize the speed of usage of the hardware (don't use older win 7 on a ryzen for example when windows 10 will run better on it.)
I have multiple bench computers (dozen or so), and some perform well under windows 7, 8.1 or 10 depending on the hardware attached to the system. and some run better under Linux.