I'm not sure that the assumptions I've made are fallacious. I read the examples on the fallacy of composition and they are things like "if one runner runs faster they can win. so if all runners run faster, all can win" but I didn't say that.
The original author made a very blanket, not at all specific statement about how "this leads to that" without any qualifications whatsoever. I have provided a specific counter-claim to that statement and asked for help reconciling. You can't just wave your hand and say "a whole economy is different than every other unit of organization in the world" just because.
It's not as though my not spending money causes the economy to halt. The more I save the more bank deposits are available for banks to lend and spur further growth. This is one of the feedback cycles you've mentioned. This works at all scales so as anyone or everyone is not spending two things are happening in parallel:
1. bank deposits pile up which all things being equal will push the interest rate down
2. real resources (oil, steel, timber, etc) pile up or are not being actively consumed, thus making them available for use
Then as the money loaned in 1 makes its way into the economy via loans, the real resources in 2 are readily available for those who secured the loans to make use of. I've just shown a situation where "deflation" leads to increased investment and growth rather than decreased.
EDIT:
If one person saves money, they can save money. Therefore if all people save money, all people can save money. That's the fallacy of composition I've supposedly made.
There's a difference between "saving money" and "not spending any money at all, whatsoever" This is because even the most ardent saver would still have rent/mortgage, utilities, food, gas, insurance, clothing, etc. The necessities make up a large portion of what makes the world go 'round; nobody would stop eating for 6 months because they could buy twice as much bread in the summer for the same price.
Furthermore bitcoin deflation isn't something that's guaranteed to happen forever, always no matter what. Many people are speculating in bitcoin right now the same way that investors speculate on a growing company, but that company's stock won't go up forever just because. At some point the exchange rate between bitcoin and the real economy will reach some kind of equilibrium and the price will level out.