Right about many newbies wanting to double in a year, or often less. That's how they end up in scams and lose everything. Investors with realistic expectations probably do much better.
I'm an expert on Warren Buffett's methods (and mod IHUB's two BRK boards). He's made about $80 billion mostly in quality stocks anyone could have bought (like Wells Fargo bank and American Express). He targets stocks that rise about 15%-20% year and then he uses a moderate amount of leverage. His real trick is his consistent buy and hold approach. IHUBers tend to trade too often, and usually at the worst time.
Still Buffett wouldn't buy GAIN or any BDC. For one thing Berkshire Hathaway itself might be considered a BDC.