Its easy to think of becoming successful in affiliate marketing with youtube channel that has lots of subscribers, it could be possible. In reality, its not easy. I personally have been there which is why podcast are much better and many have been successful with just choosing a trending topic and discuss it with a guest. However sticking to a particular niche like casino can't be get that much audience.
You'd be surprised with how many sheeps can boost one YouTuber for a long time, provided that this YouTuber knows what he/she's doing and providing good entertainment to their peers. The channel may stagnant and the referrals may also come to a halt, but it's a solid starting ground in building your affiliate network. The only catch, though, is you have to have that charisma and that personality to get yourself a flock of sheeps to carry you to success.