Ah ok...
Yes, I have observed that if I let my iPhone playing a video on youtube, it's OK.
But the iPhone does not like at all when we often switch between apps (1min on mail, 2min on twitter, 5min of youtube, ....).
Another thing related to battery drain.
I have noticed that my iPad Air 2020 drops 6/7% per day even if it's disconnected from Wi-Fi.
But, if I disconnect it from iCloud, the battery drop only 3/4%.
I don't know how iCloud can be responsable while Wi-Fi disconnected ! This is an old topic for me beacause I have already change my iCloud account in 2019 and it has no effect. It seems that something related to iCloud is running even in offline, but I don't know what. I dont' know of it is the same for the iPhone because battery use is not comparable (losing 10% per day with no use is not preoccupant on an iPhone, but it is on an iPad).
If you have any clues.... One time, I though it was homekit.... but I have no proof ! And my wife has no problem on her iPad...