But I would think that an "advantage player" would want to take every advantage they could. I wouldn't fault a professional gambler from using a Schedule C. The only question would be what legal deductions did they use? Certainly travel, meals, tips, are all legitimate as are computer time, cell phones, and even advertising if they are promoting themselves to backers/investors.
What I can't understand is why someone all of a sudden would stop calling themselves a professional after four months? There is no requirement that you have to be full time in order to have a Schedule C business. And even if a business stops after four months, you can still file a Schedule C until the day the business closes.
In fact, I don't see anything on the Schedule C that asks if the business has been terminated or how long the business operated during the year. See:
https://www.irs.gov/pub/irs-pdf/f1040sc.pdf