The BGGDL scoring system changed after I gave theory and Axxle the reigns. I have tepid interest in seeing it started up again, because the level system on isotropic effectively replaced it. I do very much love having won the league one round, though - it was also my best league to run, based on the sheer number of results each round.
I was never a fan of the point system, but I didn't fight it because I wasn't active in the league at that point (I did try to direct it in a way that made sense for the nature of the league). I would recommend not having a point system in any league you develop, and instead give priority to wins, and second place as tiebreaker.
Anyways, we always had a contingency for multiplayer games, but it only came into effect about a dozen times. It was effectively this:
If you won a 3p game outright, you earned 2 wins against those opponents (1 each), and they earned 1 loss each against you. Their net result against each other was a draw, and drawn games were always replayable. 4p games were the same, except you earned 3 wins (1 against each). If there was a tie for 1st place that wasn't broken by the rules, it was assessed in a similar way - the tied players beat everyone else except each other, and could replay their game as well. Effectively, if you won and someone else didn't win, you beat them; the standings only reflected these 1v1 contests, even though other players had significant impacts on the game.