For sustain on an electric you always have to look at where the energy from the string is being dissipated. In the case of your alder body I would put a lot of it down to that. Typically alder is not as "stiff" (elastic) as a mahogany body with a maple cap for the same mass. Maple is fantastically stiff acoustically speaking and "bright" mahogany is dense and stiff compared to alder. Sound waves travel differently in all materials and differently in all woods. Thats why a softwood like spruce is used for acoustic tops. It has a great mass to stiffness ration and sound waves travel through it well. It's all good and none of this is better or worse it's just the way it is. Each timber has a different character.. Wood makes a difference but the biggest tone factor on an electric is the pickups. Wood is next then fittings..
Okay that makes sense. So what about the other end of my string? The zero fret and maple neck. If the alder body is diffusing sustain, what's the immediate transfer of string metal-on-metal zero fret and hard bright maple doing?