Because most of my experience was with stock training size airplanes of enough but not excessive engine power, I have concentrated on management of other forms of energy available from a low AGL altitude point of view. In the "Zoom reserve" thread, JP256 well covered high altitude engine failure where slow zoom can safely trade airspeed for altitude to increase the time to execute the forced landing. He said, "A slow zoom is very useful if/when the engine fails, because you can trade off airspeed to maintain altitude for at least a little while."
Increasing weight while engine power is fixed will require increased pitch attitude to maintain altitude in stable air. Reducing the amount of fuel burn energy by leaning the mixture, necessary for best RPM at high DA, will require increased pitch attitude to maintain altitude in stable air. The nearer we get to math, based on gross weight and DA, ceiling, the nearer we get to loss of maneuvering airspeed. We can end up high enough to miss things so long as we don't have to turn to miss those things. This can be heavy in flatlands or high DA. But nature is not stable all the time so we can get into trouble well below gross weight and/or well below ceiling. Management of the common natural limited engine energy state is much easier and much safer when we manage all available energy.
The best we can do with normally aspirated (relative wind only) engines is to lean, regardless of DA, to best fixed pitch RPM and not overheat the engine by climbing at high pitch attitude. It is air cooled. Ground effect energy will increase acceleration on takeoff. Down drainage egress will provide safer opportunity to find thermal and/or orographic lift. It also gives the engine time to warm up under a lighter work load. Alternating engine climb with cruise descent will help prevent overheating the engine. Accepting free thermal or orographic lift by pitching up in up air and down in down air gets the engine into cooler air without high work load and mitigates the need for long high work load engine climbs. Using terrain effectively to provide lift when we need up and to provide headwind mitigation when we can go low reduces fuel required thus provides weight reduction.
The school solution has leaned heavily toward stabilized climb at Vx or Vy as appropriate. But. as we climb to high DA, Vx goes away becoming Vy. I'm not an engineer but have found load to similarly do away with Vx. Show me the crop duster who pitches to either Vx or Vy as appropriate on takeoff. While the book may promote Vx or Vy as appropriate , fickle natural conditions may or may not. Neither Vx nor Vy retains zoom reserve, the money in our pocket, that allows safe maneuvering flight.
Mathematical climb performance, so stable in stable air, becomes unstable and inefficient in unstable air. Dynamic rather than stable management of pitch attitude can turn unstable air into free energy. Zoom in up air with trade inefficient cruise plus dive (to maintain altitude) airspeed (why go through up air quickly) for extra altitude (zoom plus rising air shaft.) Dive in down air will trade inefficient cruise minus pitch up to maintain altitude airspeed (why spend more time in down air) for maximum safe airspeed to get through the descending shaft of air quickly.
Engine management is the starting point of energy management. Total energy management is the safer and more efficient end point...the objective.