The idea that Tohei's approach was a subset of the set strikes me as a rather self-serving position and one that would, to my mind, only be said by someone whose vested interest is in portraying it as less than what they do. I prefer to think of them as both having something to offer. In Tohei Sensei's own words "The mountain does not laugh at the river because it is lowly, the river does not laugh at the mountain because it cannot move about". The sentiment he expresses in that quote is one he directly attributed to the founder as being a part of the nature of aikido that it doesn't seek to criticise other arts. I do not believe anything Mike or Dan has to offer is something other than worthwhile and a good addition to most people's training. Nor am I deluded as to think I do everything they do, I do not. But having met and practised with a number of people who have practised with one or both of them, I'm very sure that what I do is broadly similar and totally compatible. Probably missing a few things but I'm in it for the journey more than the destination, so that's fine by me.
It seems I've returned to the same old aikiweb, and I thought for a minute there I'd missed it.
Not criticising doesn't mean not analyzing.
It also doesn't mean that all approaches are equally valid - or why would both Morihei Ueshiba and Koichi Tohei been so critical of other people's approaches in public and in private?
You'll have to ask Mert, but my thinking is that he used the word "subset" in the literal sense - the theories of martial movement we're talking about are very old and very specific, laid out in a complete and extensive manner. Many people, or arts, choose to focus on a portion of the full theory. Sometimes that's out of ignorance of the larger picture, and sometimes it's out of choice for specific purposes. That doesn't mean that what they're doing is good or bad, they just are what they are.
If you think that they have something worthwhile - then go see them. I did, as well as Tohei, Maruyama and the others. It will give you a better background to discuss them by.