IMO:

This is the area of confusion between Ueshiba's aikido and Modern Aikido.

Modern Aikido relies upon a physical version of "leading uke". It uses physical "whole body" movement (whether very small or overly large), a "relaxed" body, and timing.

Ueshiba's aikido relies upon a very internally built body that utilizes internal pathways to appropriately change the energy of the attacker. This includes using an integrated, relaxed whole body structure that is resistant to throws and pushes. This aiki body involves the use of internal spirals and power, which help create the two effects of soft/ghosty and hard/powerful.

Not to say that either is wrong. There are quite a lot of people out there who have utilized Modern Aikido very effectively or have spiritualized their Modern Aikido to make their lives better. It is only to say that Modern Aikido is not Ueshiba's aikido. They function completely differently.

When talking about "aiki", I really do think people are going to have to start defining whether they mean Modern Aikido's aiki (which, IMO, is as varied as can be) or Ueshiba's aiki (which is very defined).

Mark