Eco mode just re-maps the throttle response so that you have to move the pedal farther to get the same amount of power. Flooring it still produces 100% power. Whatever is going on it isn't the result of some inadequacy of Eco mode. With the 2013+ Leaf, flooring it and holding it there produces slightly less acceleration than flooring it, backing off slightly, then flooring it again. That applies in Drive mode as well.