I think it is more a matter of agreement on metaphors than agreement on what this illness is.
I wonder whether (the above) is the case as, I may be wrong, but your criticism of The Spoon Theory metaphor appears to be mainly based on what you said about GMG (in the 'Top Tips' thread before this thread was broken away) as follows:
The paradox of MG is that the more you rest, the more you can do.
This is counter-intuitive for most people and very hard to understand for us (and even more so for those around us).
and, from earlier in this thread:
Rest is something, when you give to your body, you need less.
Although I assume that the above is true for you, is it true for others with their GMG? Maybe it isn't true for them or is true for them but hasn't proved to be of much significance in terms of what they personally are able to do in a day (short term) or in the long term...
As you know, I am not considered to have generalized MG; I 'just' have severe 'probable OMG' and so I cannot speak from any personal experience of GMG. However, from reading forum members' postings over the years, I have gathered that pacing themselves and resting to try to recover between tasks and endeavouring to keep some capacity in reserve rather than reaching 'the edge of their abilities' plays an important part in getting the best from their day, but I hadn't gathered that resting gives a kind of 'interest/compound interest' effect. I stand to be corrected by others with GMG if I have inferred wrongly about this, of course, and I obviously leave it up to individuals to take or leave The Spoon Theory that I am responsible for posting up...
The Spoon Theory lady does convey about conserving 'energy', for want of a better word, as she does try to keep a spoon in reserve each day and she talks about slowing down too (which I take to mean pacing) and she tells of how if you push yourself over the edge one day it can affect how much you can do the next day; but it is true to say that she doesn't state that you can effectively gain more spoons to use in a day (or to put in the bank for future use) by means of resting and this may be an important omission in terms of GMG. (As I have said, I leave it up to others to comment on this if they so wish as I don't have GMG.)
I tend to use a lot of metaphors, and I have learned that sometimes it defeats the purpose and just giving a simple explanation is better if your intention is not to amuse people, but to make them better understand.
My impression is that people often resort to metaphors and analogies
after they've tried giving a simple explanation and that simple explanation hasn't for some reason hit home with the intended recipient. I know that I do; it isn't usually my first line of approach when endeavouring to explain things.
And, although obviously having MG is a very serious matter, in my opinion, I think that a quirky - possibly amusing to some - way of trying to explain things - isn't necessarily a bad thing even if one's intention isn't to amuse. It can serve to hold the recipient's attention and make the message more memorable without trivializing, but of course, that said, it doesn't mean that there aren't potentially other and better ways and means of trying to explain things, as the use of analogy or metaphor doesn't appeal/hit home to everyone and, as with many forms of communication, there is always the danger of misunderstanding and innocent misrepresentation, perhaps even more so.