What cross my mind in that argument is that, most bettors do not bother to do proper analysis before bettors on a game, there are a lot of players who are just very desperate to make money and they don't bother to research for informations before betting on a team. I argued that the bookies get the same information that bettors get because all necessary information are published in different news site. But I believe some of us here are more experienced in sports, do you think bookies buy information from leagues?
It might be possible, but at what cost? I've honestly never heard of anything like this before. Even if someone manages to buy inside information, the outcome of a game is still determined by what happens on the field. I don't know how your friend came up with this idea, but I find it quite unrealistic. I know match-fixing exists, but what's the point of buying inside information about entire leagues? Like someone else might have said, your friend could just be looking for someone to blame for his shortcomings, so he came up with this idea to make himself feel better. I wouldn't completely rule out the possibility of inside information, but I don't think it's something you can easily buy or rely on..
Now there are enough markets, and bookmakers surely have their way of taking enough profit, so why will they buy information about anything from any league? Usually after having lost, people bring arguments like this because they feel frustrated and have nothing balanced, so theories like this start working.
Sportsbetting is now turning into a big industry and uses technology, and there are more experts to give them all details, which are helpful for them about their business. People always want to have big wins to make good profit but never have results as expected, so their mindset moves into negative; it's never been stopped because gambling related fake stories will stay alive.