I think this is the wrong argument to make here. Even if it would require a hard fork, such a hard fork is not impossible. If in 100 years bitcoin is being used around the world and is worth $10 million per coin, then we can't have the scenario of the smallest spendable amount being ~$20, and so a hard fork to add more decimals may well take place. Further, Lightning network already goes to 11 decimal places and milli-satoshi, so already provides a 1000x increase in divisibility over the main chain. However, neither of these things change the fact that there a finite number of bitcoin which can ever exist.

If doesn't matter how much you divide up 21 million, there will still only ever be (slightly fewer than) 21 million bitcoin. There are infinite numbers between 0 and 1. That doesn't make 1 = infinity.