I can't see the divisions reflected in the synod as anything but inevitable. I think it was Scott Hahn who said that man cannot square justice and mercy, only God can. It's beyond the mind of man. So it's natural as the day is long that there would be these battles over the purveyors of a more merciful view versus one loyal to God's justice, and both justice and mercy are as valid as the day is long. Both are obviously extremely Biblical.
It's said that mercy does not leave the sinner off the hook, in the sense of restitution and penance, but indulgences certainly undermine the necessity of restitution. With God all things are possible. Emphasis on the first two words.