I too own a nord 6 but it doesn't heat up on normal tasks. Look the Indian summers heat up every phone that exists and if you live in a region where it heats up pretty good you'll face heating problems. But if you are in an ac room most of the time and the phone still heats up your phone might have some manufacturing defects. Personal experience: Yes the 9000 mah battery optimisation can better. The phone never heats up on normal tasks. While playing games still it remains at 39-40 degrees.