All these compounds conduct heat far better than air, but far worse than metal. They are intended to fill gaps that would otherwise hold air, not to create a layer between component and heatsink—this will decrease the effectiveness of the heatsink.
Excess grease separating the metal surfaces more than the minimum necessary to exclude air gaps will only degrade conductivity, increasing the risk of overheating.
Our Chinese factory is just sloppily brushing it all over the IC and the heatsink, and I think it's more harmful than helpful. Is there a recommended procedure for applying it? Are there machines for applying it quickly in mass production?