No need for PID and all that complexity.
next step is to add a fan in the floora) to aid cooldownb) might improve ramp-up as well!
the cool down is even slower
I use a 4 element oven, 2 top & 2 bottom, 1500W, observations with k-type thermocouple to digitlal multimeter are that it heats up fast enough.skyjumper found the same a while ago - 3 elements not quite enough.
Simply opening the door is probably causing a faster cooldown than 6°C/second, which is a excellent way to damage components.