Assuming you normally maximise Con you end up a few points ahead under the proposed system if you go with point buy

A SAD class like fighter can now afford slight bumps to the secondary stats:
15, 13, 15, 8, 12, 8 >> 15, 15, -, 8, 13, 8

A MAD class like cleric sees a similar improvement:
14, 12, 14, 8, 15, 8 >> 15, 13, -, 8, 15, 8