Why give the ability to lockout classes for Raids?

[Alistaire]

People are addicted to contributions, rather than the actual damage at the end.

You say that like it's a bad thing.

In the end it's simple, if BLM has highest personal dps yet doesn't contribute as much of a combined personal+boosted raid dps to end up on top with that considered, they're not the best job to take.

Or to make it even simpler, just roundabout numbers, say a BLM has 5000 dps but a SMN has 4500 while boosting the dps of the rest of the party by 1000 (combined between the 7 people, not 1000 each), it should be pretty easy to figure out who wins.