Insulation, more efficient compressors and so on are all very well but the biggest efficiency gain for freezers are chest freezers vs uprights or at the very least very well made internal drawers. Basic physics, the cold air (which is heavier) cannot escape so easily from a chest freezer whereas uprights waste a lot of 'cold' each time the door is opened. That's why they big American style monsters really should come with more compartments and four (or more) doors so less cold air can escape each time you open the door.
That plus having something the correct size (a full fridge or freezer has less air to rush out when you open it). I can easily see how an old 80L freezer is going to be better than 240L one if the large one is mostly empty.