I seem to remember this downwind/into wind argument regarding energy as having been done to death before and it all has to do with the frame of reference.
I know that turning 180 from downwind to into wind won't give me extra energy or make me climb if I maintain attitude, airspeed and power - I will roll out with the same airspeed but a much lower groundspeed. Done it more times than I care to remember without ever having an unwanted climb or having to reduce power.
Aircraft crash turning downwind at low level because the pilot tries to maintain a constant groundspeed in the turn and washes off airspeed.