@NotATether - I bet a lot leagues, mostly lower levels of England, Germany, Finland, Sweden, Portugal and first levels in Asia and South America.
As far as I know this gives you some credibility. I have not bet on sports betting other than the odd bet from time to time but I have been interested reading articles and watching interviews and what I usually read from successful bettors is that they try to find a niche in the less popular leagues.
In my opinion, this is the path that players take as they gain experience. They start playing in the top leagues, of course, and then gradually begin to understand that playing in lower-level leagues is sometimes much more interesting, and sometimes, if you're lucky, it brings relatively more profit.
And by the way, the pleasure of betting on games in lower leagues, in my opinion, is about the same as playing in the top leagues. But at least it's no less, and sometimes even more.