Maybe you should calculate the actual wattage of the element, just to make sure our assumptions are correct. Disconnect the element and use a multimeter on it to measure the resistance (R). then just (230^2)/R = Wattage. Your outlets may not be fully 230V and the resistance of the element probably varies by about 5% between room temperature and 550C, but this will ballpark your wattage. Once that's confirmed we can move forward again, with what the problem might be, because im stumped.
Hi! Just checked the resistance on the element with a multimeter - 36 ohms confirms the element to give an output of 1500W-ish. So that is obviously not the problem. The voltage in my apartment is definitely 230V.
Any ideas why this element gives such a poor performance compared to the stock 600W, then?