When it comes to building the actual modules for the ship, like weapons, sensors, armour plating I do strongly agree their manufactured in a mass basis. Not just for new ships, but for replacement parts and resale.
The primary bottleneck I can see is the installation and construction of the actual superstructure and armour modules. I can't see it being a speedy process, but applying them as modules instead of 'build-as-you-go' basis is a time efficient process.
While a zero gravity environment greatly enhances the movement of incredibly heavy components, the lack of superstructure robotic equipment such as cranes and massive 'welding' devices, at least just looking at the construction facilities would slow down the process.
Current construction methods are good, but its far from the best without sealed and dedicated hangers that can handle multiple capital ships, up to and including carrier class.