The first week i had my 7+ i tried to find out what app's were draining the battery, because it seemed to drain quickly.People who are getting great battery life sure not watching YouTube
Your right about YouTube, video on FB, and 4K video really drain the battery.
I now occasionally get on YouTube with my 7+, usually use FB, but unless i'm going to keep a 4K video i change to 720P. I don't need to see notification's on a locked screen every minute of the day, which also uses a lot of the battery, so i turned that off.
There are trade off's using any iPhone. I find myself using the 6s+ and 7+ more, and my iMac or macbook air less. But when i know an app drains the power i set it down, and choose one of the other's. I know when i go to YouTube i'm going to be there for awhile, so why use my cell.