I'm going to stop because I think I've made my point (perhaps poorly) and I feel this discussion is becoming a distraction to your main topic.
I'm trying to understand what was your point. That it's obvious supply isn't affected by demand? But it is, in most cases.
Consider Dogecoin. It is inflationary, so I would assume that you would consider its money supply to be elastic.
No, I wouldn't. It has a completely inelastic supply. The lack of deflation doesn't make that false. The block subsidy doesn't change with the rise in price.
The X-axis is the total quantity of money available on the market
You only count the quantity that
can be available on the market.
(the problem is we don't know the real purchasing power of bitcoin because the price of bitcoin is always thought in fiat terms)
Why don't you know the real purchasing power of bitcoin? 1 BTC = ~$41,000 currently. The purchasing power of $1 is equal with ~2,400 sats.
No, it is highly significant, because it makes Bitcoin supply unresponsive to the changes in demand. Gold and other assets lack this feature.
Look where I've quoted you:
A difficulty adjustment is what makes the bitcoin supply barely responsive to the changes in the demand for bitcoin.
Yes, it's true. Yes, if the price fell by -50%, the supply would take longer to be increased, but that's until the difficulty retargeted. All I'm saying is that this is not the canon nor a significant factor.