I'm sure there are professional gamblers out there and I'm also sure, with the big wins that sometimes get it will be enough for him to pay for his daily living needs or maybe for the next few months, at the same time will be used again for betting. So, I feel that pro gamblers are gamblers who have big bankrolls so they don't worry too much about losing, because in the end they will definitely be able to handle it with their experience and strategy.
I have seen and known people who have gambled for a living but for the most part they are already rich enough to not even care if they lose as they have businesses to back them up. Some gamblers I've known have built and started their businesses with their gambling winnings and stopped working their jobs to be a full-time gambler. The key to have a profession on gambling is the have patience (have control on yourself) and know what to only gamble. Anyway, I know some people who've gone broke due to greed and losing their patience as they've bet stuffs that made money for them which isn't something ideal.
Gambling as a profession? Maybe its possible if your pro in skill based casino games just like texas holdem poker because you need high level set of skills and experiences, non-skill based casino games are impossible to earn a living because you will only rely on pure luck.
You are correct, among the gambling games the only one that required skills is the poker game while all others are just gambling for luck. This is the reason why many professionals do end in poverty after their involvement in gambling. We all agree that gambling make have made thousands in this industry also it has destroyed and still destroying thousands in this industry.
Most gamblers that have made a living on it rarely gamble on luck based games as they won't have much advantages on it unlike skill base games where they can rely on their own knowledge and strategy to win such as card games.