Well I think it could be used effectivley by spectating after you played the mod of your choice. You could play a fairly large amount of games if it was just 1 or 2 other players in the lobby. But potentially not given the points you made about the penalty. But I don't think this matters to much.

I feel the biggest issue is that the ranking system isn't a 100% equal playing field even if a player exploits this for just 10% of their games. If Toribash want to attract players to the competitive side then it needs to be a credible system in order for players to invest time playing it.