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.
And if there is a public participation on the post of the video then there is highly chance to increase audience day by day and finally refferal will increase too. Important thing on this case is to use perfect keyword.