Google it. Maybe you got lucky I’m not the only one having this problem. It’s documented all over that 11 almostcuts the life of the battery by half . Just google it. I thought it was just me too. Till I did some research.
Google "abducted by aliens". Now, tell me if that means all of those people were abducted by aliens. Googling something is, in and of itself, not research.
No one is saying you don't have a problem with your phone. However, if you jump to the conclusion that it's because of the update, and then don't do the requisite troubleshooting, you may find that you continue to have a problem even after the next update and the one after that.
So, you can complain or you can see what you can do to resolve the problem.