To me, the arbitration process is a falsehood. Why did he get a reduced sentance from a rule-based 10 game suspension? It was not a suspension based on a judgement from Watson; he was caught with pine tar on his glove.
If Donnelly's suspension was "rule-based" than he wouldn't have received a single game. The rule MLB claims he violated (3.02) reads:
"No player shall intentionally discolor or damage the ball by rubbing it with soil, rosin, paraffin, licorice, sand paper, emery paper or other foreign substance... if the pitcher delivers such discolored or damaged ball to the batter, the pitcher shall be removed from the game at once and shall be suspended automatically for ten days."
So as Donnelly never delivered such a discolored ball, he should not have received the 10-game suspension.