it might be that you have used a different theme and no its not a hardware problem at all its a software problem because if the screen was blurry the brightness slider would also be blurred o recommend you try to change to your default skin or launch...
is your storage full? mine is also getting slower but not noticeable maybe close out apps and clear the ram or it might be that the wifi is slow i never had a issue with my j7 pro with wifi and the update might come around in September
