Arcane hypothetical edge cases are unhelpful for exposition. It's easier to look at the conventional alternative: everybody in the world uses a means of payment which diminishes in value at a slow but stable rate. Now the average person that invests in production gains, and the average person holding cash is incentivised to convert that cash into something they want or funding the production of something others want. Isn't this better?
(1)strictly speaking we're better off looking at money as a flow, in which case the velocity of circulation comes into place, but a fixed money supply certainly wouldn't induce that to increase....
This statement is wrong, because you measure profits in money rather than value. With bitcoin the amount of money in the economy stays the same, true. However the value of each unit grows as soon as you invest and produce something useful that people want. This means, you may receive back even less than you invested in absolute units of money, but more in value.