I used to manage a few extruders; most of the older ones all had individual temperature controllers for each zone from, say, Eurotherm or whoever. There was one that was all PLC controller with SLC505, but we compromised: any new ones sourced all had individual controllers for each zone (the plastic engineers wanted this) but I would get the comms card option (usually Modbus with RS485) and then string them all together and feed them into a PLC. I would use the PLC for master functions only: setpoint changes, startup/shutdown procedures, data collection, alarming, etc. But individual zone PID control I just left to the experts - the little DIN mount temperature controllers.
If I had to do it again, this is the approach I would prefer - individual zone control, then all tied together through a fieldbus to a PLC/HMI/SCADA system.