That sounds reasonable. Once the liquid and pot get up to 200, the power you are adding is equal to the power loss, and so there's no more power left to raise the temperature.
Contrary to what is normally posted about required power for a brew kettle, there is more to boiling than raising the temperature to 212 degs. The actual act of converting liquid to steam itself requires power, on top of the power required to maintain 212 degs.
Quick note about the electrical power in your situation. If the outlet is wired wrong, and one of the hot legs is actually neutral, you are only supplying 120V instead of 240V. The power is proportional to the square of the voltage, meaning you are only getting 5500/4 W, or 1375 W. That seems reasonable, considering your results. Check the outlet. Between the two hots, you should measure somewhere around 240 RMS.
I was about to suggest the same - check the wiring that there hasn't been a cross over in your control box for the element swapping one hot for the nuetral.