If that weren't the case, the TSA would have simply banned all liquids.
By all indications, the 9/11 bombers were very high on the AQ food chain. The underpants bomber didn't get tens or hundreds of thousands of dollars wired to him before the op; he was a shmuck, in a strategy designed to weaponize schmucks.
If a TSA measure doubles the manpower required to carry off an AQ op, it is almost prima facie "effective". Is, I think, the logic you'd deploy against the "combine the 3oz bottles" argument.
Of course, we're now talking about a _conspiracy_ - and a conspiracy of four average people is 100x more likely to be discovered by a intelligence team than a single attacker.
So perhaps it's the forcing of attacks to be _conspiracies_ is the goal of allowing only small amounts of liquids.
Regardless - I think we can all agree that it makes liquid bomb attacks substantially more difficult than simply allowing people to carry on as much liquid as they chose, and therefore opening the door wide open to a lone attacker just blowing up airplanes at will without possibility of detection.