Well, I know what I was asking, but let's make sure I know what you're asking. Are you meaning "Aiki model" as it differs from an "IP model"? I have not personally experienced any "alternate" model that I felt impacted the practical application, so my answer to that is "It's all just really good technique."
My belief is that the mental constructs merely inform our physical training. Take Tai Chi as an example, when they envision smoke or fog moving through their body and into the ground. We all know there's really no smoke going from you into the ground, but maybe it makes you harder to move from a spot.
My concern is that one there- Does being rooted into the ground have martial value? It certainly assumes you can take a punch! People have said moving in six directions has to precede some physical movement. That would just have to slow down reaction time.
Or maybe it's like board breaking. Great demo, busting 12 bricks with your bare knuckles. But nobody is going to let you take seven practice swings and focus your Chi before you hit them, right?
When I am executing waza, I know where uke's center is. I can feel it. Ukes don't outrun my ikka jo. They float in Shiho Nage. I'm not bragging- I'm just saying those effects are available through other training methods.
So let's introduce a "Technique model". I am starting with just as much evidence as anybody else, and I can say, "It really works! Go train with Demetrio Cereijo, then get back with me if you still want to argue about it."
I think we have a kata model. I would advocate that, in fact, a kata-based teaching model is the main teaching model in aikido, as evidenced by the testing process. And the conventional argument to kata is exactly your point, if you do it well enough, long enough, you will be good.
I am trying to stay away from getting into internal power. From my experience thus far, there are a number of different methods to develop internal power - even the people teaching internal power are still discussing which ways are better or worse. I am trying to pick up at a point of "aiki is driven by internal power," not taking issue with necessarily how you develop internal power (only that you encompass these exercises).
Specifically addressing your comment about grounding... First, I think "grounding" is great example of an exercise about which internal power proponents debate. Regardless of the debate, I think the idea is not really to be affixed to the ground. Rather, the idea is more similar to the concept of creating a store of potential energy by compressing the lower body. Think karate punch, where you screw your feet into the ground to create a compressed energy that goes into your punch. Messisco sensei uses the imagery of floating in space to create this potential store; in space, you cannot "push" the ground.
I think there is some value in claiming the tangible benefits of a physical kata and clear objective criteria for "correct" movement. Kata is a great map of what to do. But, its a contrived shape upon which we agree to practice. Kata is not randori. In judo, for example, even for many excellent practitioners competitive judo is not kodokan judo. O soto gari as kata rarely looks like O soto in competition. So, is your opinion about brick breaking extended to the role of kata in randori? Is our randori partner going to give us 4 opportunities to throw them? Or, are we taking about an exercise that is intended to produce a result with enough practice. For example, is practicing board breaking in karate really about breaking boards? Or, is it really about focusing your efforts on correctly punching, the feedback of doing so resulting in your bare fist breaking a board. For someone who can do this exercise with regularity and needs no practice swings, what effect would that have in kumite?