I agree in order to develop good characters of out of gambling first we need to be capable of learning out of anything. Addicted gamblers will never mind about learning anything while they are gambling. Such type of gamblers will keep on gambling regardless of whatever outcome they are facing so when they are not focusing anything outside from gambling then you cannot expect them to be developing good characteristics from their activities.
Overall, the positive evolution of gambling is possible only for the gambler who are all open to learning. If you ignore everything then there will be no room for any of positive things.
Which is why even if I think the OP is not wrong and you can learn some important life lesson out of gambling, I think the majority of gamblers do not really learn anything substantial out of it, and this is because most people are just interested in having some fun and nothing more when they gamble, so even if a life-changing lesson could be learned from what they are experiencing it is difficult they will do so as that is not their intent.
Problem gambling is always terrible. Those who are addicted to gambling will never want to admit it cause they can't realize it. The OP may have tried to point out some nice things but the problem gamblers can't learn from these things, Only those who are thoughtful and willing to come out of the problem gambling can learn from these things.
this is the ego of the gambler who thinks he is not a gambling addict but it is different from the reality because they are indirectly included in it

But on the other hand, there are experiences that must be used as a reference so that terrible things don't happen again. But as you said problem gamblers are not aware and will always get to the worse.
Denials would be there even though its already that obvious that they are already addicted to it on others perspective and it a common behavior for someone to make out some denial that they arent addicted but the truth is that they are spending more than that they get used to.Gambling is for pure entertainment but people do really excessively dealt with it on a different manner which
do end up on a disaster.
If you do just know on how on how to control yourself and able to realize up on how things do work then you would really be able to save up yourself from trouble.
Try to stick on how things should be treated out.