While there are many definitions about what it means to be a professional, one of them is simply about your ability to make money in any activity, so professional gambler is indeed the correct term for the people that can make money with gambling in a consistent basis, now the issue is that for every single professional gambler out there, there are hundreds of people that tried to achieve the same results and they failed to do it, as hardly anyone hears about their failures.
Alright buddy, I Don't want to be disagree without your opinion because your opinion is also right on the other point of view.
But what I mean professional means is connected to professions and professional means an person who are is well skilled on that sectors. And in this point of view we can't assume the gambling as a profession because gambling is all about luck and it is for only entertainment purpose.
And that is why I mentioned that here the word should be used responsible gambler.