Aiki and high level internal is not something that can be proved in debate or argument it has to be felt and expressed in action.
High level internal can be shown. I know because I've trained with a recognized high level internal expert for a number of years. He can do a number of very impressive things. However he will be the first to tell you that they are all a product of angle, leverage, body weight, natural elasticity of the tissues and alignment.
You can see all of these things demonstrated by modern sport martial artists as well. If the definition of Aiki is internal martial arts, then we are going jump out of one pot and into the next. Because (Chinese) internal martial artists are having this same debate.
Because the martial arts are of a physical nature, there must be a tangible representation of any skills that are useful. This thread, posted recently:
Shows the power of suggestion at work. The Sensei here is demonstrating great control over his students. This is a useful martial skill. There is a tangible representation of this skill, his students are willing to do all number of things for him. I think this is just one of the skills that Ueshiba was very proficient in.
Defining the power of suggestion as Aiki is a reasonable one. No more or less valid then angle, or timing.