I think that approach is valuable and "softballs" are only bad if you're assuming Rogan is a journalist, which he isn't. He's a comedian, an entertainer, and a conversationalist (and, of course, a martial artist). People tune in to hear him have interesting conversations with interesting (and often wacko) people.
That's his appeal--few people would be interested in hearing him grill his guests. We have CNN for that. Saying he "lobs softball after softball at them" is true but not really a bad thing given that he doesn't claim to do otherwise.