Stolen parts are always going to be cheaper unless the cost of producing the parts is lower than the disassembly cost. That could happen for screws but it’s never going to happen for the advanced components which are why the devices are actually being stolen.
What does that look like? Stolen parts will always be cheaper.
The warehouses full of people in Shenzhen tearing down millions and millions of stolen iDevices would still be chugging along, inserting stolen parts into the supply chain.
Apple enforcing DRM on parts is very much a pro-consumer move, steadily taking us towards a world where a stolen iPhone will be worth nothing.