Why the bigger penalty? Well, it's been covered here at length, but one more time then - the additional charges against A-Rod are that he:
1) enticed other players to use PED's.
2) obstructed MLB's investigation.
Obviously the evidence of A-Rod's transgressions was strong enough for the arbitrator.
The early expert opinions we've seen indicate that A-Rod's court appeal is extremely unlikely to succeed.
Yes, MLB appears to have played dirty a bit, but that's a molehill next to the mountain of A-Rod's wrongdoing.
All he's doing now is following in the ignoble steps of Lance Armstrong. It ultimately failed for Lance and it's going to fail for A-Rod just the same. He's done.