There is no strategy or skill that a professional gambler can master to become successful. Even some gamblers who are not recognized as professionals have better gambling success stories than so-called professionals. It is a function of "whoever gets lucky wins the most." Personally, I subscribed to some platforms in the hopes of increasing my winning rate, but it turned out to be the same story of not winning or almost winning. Even the experience that these so-called professionals have gained over the years, as you mentioned, does not give them an advantage over the bookies.
I am curious how you come to such conclusion, that if you gamble on more than one gambling platform, you would win more often. Did it comes as inspiration after seeing other gamblers? Because in theory, your win chance should stay the same, as each platform offer same games, rules, often odds.
For example, the popular saying "gamble with what you can afford to lose" comes from an experienced gambler who understands that nothing is certain in gambling, so a gambler must be conscious of his stake.
I believe that comes from a person that understands value of the money, he might be a newbie in gambling, but he understand how money give opportunities and open previously closed door, and he knows how hard it is to get them.