If you can’t read fast, you’ll never understand how people who do can fully grasp what they’re reading. But I assure you, we do truly appreciate and get the feelings conveyed in the book. I prefer to read more slowly because it’s relaxing, but I can read fast when I need to.
I would contest that retention is not a factor regardless of speed or even comprehension. In order to retain something, one has to read it several times (unless they are a rare sort who has eidetic memory).
Sounds like a Chewbacca origin story.