I'm largely in agreement with you. I don't think its terribly effective to tell people what they can and can't do. If we don't want people to gamble, making gambling illegal isn't going to move the needle meaningfully and it's probably going to increase overall harm. See, for example, the war on drugs.
But we can move the needle by regulating the supply side of the equation and the more infrastructure intensive the supply side is the more effective regulation is. Banning the sale of leaded gas, for example, resulted in a pretty painless transition away from lead in gasoline. We didn't need to arrest people using leaded gas; the inconvenience of getting leaded gas was more than enough to get people to convert.
That's the approach that makes the most sense for online gambling too. We don't need to be kicking down doors to card games or frog-marching seniors out of bingo night, but we probably would be substantially better off if it weren't legal to develop platforms and services which are specifically engineered to engaged young people and nurture in them a crippling gambling addiction.
And we can say "oh, but why can't you just convince companies not to build those products without the threat of government force" but building those gambling products, or putting heroin in the Big Mac special sauce, or handing out cigarettes and alcohol at middle school football games is a fantastic way to make giant buckets of money at the expense of people's lives and nothing short of the threat of consequences exceeding those potential profits is going to convince a profit-seeking corporation to pass on all that money.