Some latest fundings:
App installations are causing FpsCentralContr (FpsCentralControl service) to kick up CPU usage to 95%, and it stays there, doesn't come down. Even after screen is off it stays there, eating 95% cpu time.
Remember, even manual apk installation from file manager is triggering this behaviour, so not completely dependent on Google Play Services, IMO at least.
Due to this, cpu is kept clocking at 2.96 continuously, which intimately reduces battery life and causes device heating.
And these high temps in turn result in slower charging speed even on 30w charger.
Ps: following observations were made using ADB tool and armoury crate for temp reading, device was not rooted, and
@FiREPLAY guided key stuff.