i can tell you it just the same i have this app called cpu dasher x and it has its the same cpu speed when i first i first install it on ios 12.I suspect Apple increase internal clock in 12.x - which made overall system speedier and faster (even compared to 10.x) with the cost of shorten battery usage. They are preparing foundation necessary for new functionalities (ie News+ in 12.2). In my opinion, this is fair enough, but somehow Apple needs to mention this in release note so everyone will know consequences of upgrading.