I have been thinking about this tank healer shortage for a awhile now, and it dawned on me
2 tanking class
WAR
PLD
5 DPS class
BRD DRG MNK SMN BLM
2 Healing class
WHM SCH
So it seems like a balanced group should be 9 (instead of the current 8). However, since it is 4/8, the ratio of 1-2-1 is broken (should be 1-2.5-1), which leaves a .5 DPS class without a job per 4 man dungeon.
This seems pretty small, and it is, since DPS queue times may have 5-10x tank/healer times and can't be accounted for simply on a numerical basis for the classes.