You forgot that the blacksmith saved 10BTC before the deflation happened. Giving his saved BTC more purchasing power than they had, making him able to get a bigger piece of the rare goods.
Wrong. You can't take the price level and multiply by the quantity to determine what the saver would get if he liquidated his position. The people who own millions of bitcoins can't liquidate and realize $15 for all of them. Only the first sales would fetch $15, and the more they sell, the lower the price.
If someone bought a lot of bitcoins, enough to drive the price up to $100, then almost all of his purchases would have occurred at a price below $100. If he takes the market price of $100 and multiplies by his holdings, he will show a fake profit. This is what you are calling "increased purchasing power". But he cannot liquidate them at that price.