Have you tried resetting the phone? I know that any iOS build has it's bugs and issues but I have a 12 Pro and don't notice any of the issues that you outlined. Battery may be a little worse but certainly not that bad.I have a couple of issues after going to 5.1.1 on my 12 Pro:
Great "upgrade" Apple! I had none of these problems before. Does Apple even QA test before they release??
- Battery drain is really really bad, it's maybe 30% quicker drain than before.
- Sometimes it takes 3-4 minutes to restart the phone.
- Phone has issues connecting to WiFi after restart.