Bitcoin is based on an increased demand an a deflationary supply, however that eventually leads to a coin that people don´t use to trade or to transact. What do you think that the emission rate of a crypto should be to be used as a coin? Any automatic mechanism to adapt exists?
[/quote

Deflation happened when the change in prices turns low or negative, when the change in one period is lower than the previous period. When there is deflation the bitcoin people will hold their coin and tend not to spend to have reserves for possible financial losses and will wait for the prices to go up again.  Actually it doesn't matter
how many coins there are but how much is the value of the coins when changed to other currency. Ironically bitcoin has no deflation problem because it is a channel for making normal currency transactions, taking over fiat currencies.