I don't think of a book as delayed gratification because books don't take that long. Consider, you click on a link and get a video your first thought is "do I have time for this?"
Watching a MOOK's is a huge commitment where reading a book covering the same material is fast. Video brings great value and can be more relaxing, but reading is generally just faster.
Strongly disagree. Reading a book requires patience and comfort with delayed gratification. Not only does it require it; I think it also develops it.