I've played in BCA and BCA type leagues and none of them used any rating system. Not saying that there aren't any BCA ratings systems, because it appears there are. Evidently, it just isn't very standardized. Some do and some don't. The problem with no rating system is that in most cases it's easy to tell who the stronger players are, and thus who the stronger teams are, and therefore it's almost predetermined who's gonna finish in the top positions.
The APA format is designed for league play and thus favors a better fairness aspect. It gives virtually every player, and thus virtually every team at least a chance of winning. The design of the league is to narrow the gap between the chance of a stronger player winning vs weaker player.
So, when an APA 6 plays a 3. Or an 8 in BCA type vs a 6. (Numbers arbitrarily chosen).
When the players play straight up even race, clearly the advantage always favors the higher player. If you were gambling if you had half a brain, you wouldn't bet for the lower player, there'd be no point. You'd have to give some odds, in order balance the scales at least somewhat.
Whereas with the APA rules and race format, the advantage is still to the stronger player, but the other player would actually have a reasonable chance of winning. If either player misses a bit more than normal, then they usually won't win.
Usually in gambling situations, the dominant player has no desire to give up any advantages, so the BCA rules format will almost assuredly prevail in that situation. The stronger player wants a pre-determined outcome, and wants to be rewarded.
Sometimes the stronger player will have to give up weight, just to get the opponent to play. For example, wild 8 in 9-ball, or games on the wire. Obviously, in any such weighting scenarios, some will cheat or sandbag or manipulate the odds in order to try to skew the results. So you always have to utilize methods to protect against such behavior. Often times it's something as simple as just spread the word...
And, to anyone with any level of skills, bar rules are just ridiculous and subject to many disputes, especially in gambling situations.