I agree having multiple devices is best depending on what you are doing.Same here. I cannot stand watching a clip on my phone that's longer than 15min. As a few have mentioned, the iPad is much comfortable to use for a few hours than a phone whether it's for watching videos or viewing large photos.
Personally a smartphone cannot replace the iPad, iPad cannot replace the laptop and the laptop cannot replace the TV.
I enjoy roaming between 4 different screens depending on where in the house I am or what I'm doing.