I'll play the other side of this argument...
You get your prefect system of composting
and greywater recycling up and running. All is well until five years down the line when you get hit by a car and spend 18 months recovering. You can no longer get to the garden
to rearrange soaker hoses and infiltration pits for your greywater. The compost
toilet is defunct because you cannot empty it. You now have a grey water system that can't be maintained and need to find an alternative for the compost
Yes, they standard system may be overkill, but it is like an insurance policy against the worst happening - your property will always have a system that works and does not depend on the will/fitness of the owner/operator.