but the aircraft seemed only to climb due to the curvature of the earth
Don't necessarily blame the aircraft. It could be a combination of other factors. Typically pilot technique. For example were the control movements smooth and coordinated? Harsh control movements create drag. Were the cowl flaps extended when they need not have been for the temperature of the day?
How accurately was the airspeed flown and was excessive elevator control being used - in other words over-controlling.
Were the flaps fully retracted immediately the go-around commenced or was there a few seconds delay before flaps were selected up?
Was the nose raised immediately go-around commenced on one engine when in fact the aircraft will need nose down during the initial go-around in order to maintain the desired speed as drag is removed. In other words the single engine go-around procedure is different to a normal two-engine go around.
Depending on the density altitude at the time, was the mixture full rich on the live engine or leaned to best power which will give you a better rate of climb under certain density altitude conditions.
Any combinations of the above factors will often degrade the rate of climb single engine. Pilot technique and knowledge of these factors is vital.