Why are you searching for internal strength? Why is it missing from your Aikido training? Why are you going outside your art to find it? When I read the threads about this training it makes me wonder what you are lacking that you have to go find it.
Once when I was joined in the conversation I was told I don't have it because one of my students doesn't have it. If you asked me about that student I would agree. His heart was not in it. Aikido training lets your inner strength out. You don't have to go to an expert to find it.
Aikido training for me is a whole practice…the development of correct feeling is just part of the process in becoming what Aikido is molding me into. Are you missing the point in your impatience to be the strongest person alive?
Well, I think this is where the current initiative amongst aikido practitioners to get some skills in internal strength will start to pay off - hopefully. On one hand you have people chasing internal strength, saying, "Yes!! This is what I was missing!" on the other hand you have people saying "We already do that!" and then (assuming this is akin to the many-handed giants of greek myth) there are still other hands "Not important", "Those people are mean", "Aikido is love", "My association forbids it", "Shut up and pay your dues", "I just train because I enjoy it - leave me alone", etc.
I think it's great that there are different flavors of aikido, but I think it wouldn't hurt if they were called out as what they are when measured against some objective standards (no idea of what those would be, either) . . but if you say that you do internal strengh, there's some basic things you should be able to demonstrate. If you say that you train aikido as a martial art, then some modicum of martial integrity needs to be present, if you say aikido is moving zen . .etc. The same. If the argument is that aikido is a blanket that encapsulates all of these things (which, being "formless" I can see how that gets rationalized) . . fine, but then it's even more important to have standards and some objective definitions around how each of the facets work.