So I looked at some numbers.
| IP | FIP | WHIP | K/9 | AS | CY | WS | bWAR |
Mussina | 3652.2 | 3.57 | 1.223 | 7.1 | 5 | 0 | 0 | 82.7 |
Halladay | 2749.1 | 3.39 | 1.178 | 6.9 | 8 | 2 | 0 | 65.6 |
K. Brown | 3256.1 | 3.33 | 1.222 | 6.6 | 6 | 0 | 1 | 68.5 |
I include Kevin Brown because he had a Hall of Very Good career, got 2.1% of the vote his one year on the ballot, and dropped off into obscurity.
By almost every statistical measure, Kevin Brown was a vastly superior pitcher to, say, Jack Morris, but that's a whole other post. And he never sniffed the Hall.
I think the only thing that makes me lean Moose > Halladay in this exercise is giving Moose some credit for being in the AL East his whole career.
But my point is Mussina wasn't THAT much better than Kevin Brown.