I don't know what the US law say about gambling and promotion of casinos by celebrity but if this were in my country, the case will be thrown out for lack of merits. Drake promoting a casino does not make him liable for losses anyone will incur due to irresponsible gambling because the casinos always add the disclaimer that users should gamble responsibly. The other charges added there about Stake being illegal in the US is false and for adding that to the lawsuit, the claimants may be in for another round of litigation by Stake if they chose to do so.
Maybe the person who claims stake is illegal has a personal issue with drake and think they should extend it to the company he's promoting cause I really don't understand the lawsuit, if Stake was illegal they would've been banned from this forum by now but then they're still running an active campaign which they've been promoting for long. Just like you've said, the case has no merit and im sure it would be struck out especially if drake didn’t use stakes platform to launder money or do anything fraudulent.