Former MLB commissioner Fay Vincent told me that the only way the Marlins are worth $1.3 billion or close to that is if gambling is legalized nationally, which he believes would create a lot more revenue. He believes it’s likely to happen.
Where the “flood of revenue” that Vincent is talking about will come from isn’t clear.
The most likely avenue for legal sports betting happening quickly is the Professional and Amateur Sports Protection Act being struck down in court and state-by-state regulation occurring, a la Nevada sports betting. That is difficult (or impossible) for leagues to monetize directly. They probably aren’t going to get a cut of any revenue that comes from new state laws.
But certainly the rollout of sports betting would lead to the ancillary of more interest and higher television ratings. That is something the leagues would benefit from.