They will put bench it on a 4k rendering of their video, they test battery by running it down (time lapsed). What day to day do you mean?
Surfing and email? That's just not intensive enough, if a 2min clip showing rendering kills 2% of battery, just scale it up. You don't need it to render non-stop for 5 hours.
I think you're probably being intentionally dense, but I'll go along. I'm not saying that rendering is a bad test, it's just the main one they focus on - and frankly for a huge amount of people it's irrelevant. Most people don't work off a Macbook Pro and render 8K RED RAW footage, or PRO RES footage, and then sit or as MKBHD in his latest video 'need to be able to edit 8K on the move' - I've worked with huge companies who do this, they have render farms for this reason. It's not a requirement for the editor to sit and wait whilst their laptop does it. I dare say the YouTubers test their video editing workloads well, but it's a tiny percentile of what people use it for. What about complex compilations, how does it compare compiling huge software libraries in comparison of the previous gen, what about ML/DL advantages in a real world environment in comparison to the graphs Apple provide.
There's hundreds of other scenarios which never get a mention, but if you want to think that YouTubers who exist only to get views, subscriptions and likes do a thorough test of devices and what they're capable of and actually resemble real-world Pro Users then feel free.