Competition is essential to competitive sports (the only ones we could be talking about), so removing competition ruins the sport, independent of the idea of entertainment
But now you're back to the original, curiously unanswered, question: Is there really that much gambling going on in the "little leagues"?
If not, for what reason do you think they are going to start rigging it? Hell, not even the WWE's explicit rigging has motivated high school wrestling to move in the same direction. This idea you have that sports are going to lose their competition seems to be completely unfounded.
Professional leagues may choose to rig or otherwise modify their events as they prioritize entertainment over sport, but they've always done that. In that sense, their play has always been "ruined". But that entertainment is not the sport.