I definitely do agree with you: rock is more influential and positive to the listener.

However, it depends on where you're looking. If he's citing those rappers, then he's wrong - those guy aren't positive at all. But there is some oldschool and underground rap that is a lot deeper. Although the mentality still seems to be that you have to rap about "sex, money, drugs, and fame" to a certain degree. It's like a quota you have to fill or something. I'm not sure, I used to be a big oldschool rap fan when I was a kid. ANYWAY. I do believe rock is more influential to the listener, and certainly more positive. How many kids learn instruments after hearing "Moving Pictures" by Rush, versus how many kids start rapping after hearing "The Black Album" by Jay-Z? I know Rush made me learn drums, but Jay-Z never influenced me to rap. As per positivity, I think rock musicians usually at least try to write deep songs. They don't always succeed, but I mean, writing meaningful things is sort of expected of a rock musician, it's a goal. If you don't, you're ridiculed. When rock musicians try and sing about how much drugs they take, or how many girls they score, they're usually labelled as extremely try hard. Nickleback's "Dark Horse" album is a wonderful example here.

"Now, I'm not a fan of rap. For me, rap is just bragging, isn't it? It's just, 'I got a big *** house, I got a big *** car, I got a big *** woman.' Alright mate, stop showing off. Why don't you just read off your shopping receipt and lace it with misogyny? That's all I can hear!" - Russell Howard on rap.