OK, lemme approach this from a different perspective:

Bitcoin isn't absolutely scarce.

If it were, any change to the final supply would be absolutely impossible. Yet some, including a few major figures like Peter Todd, want to change the final supply, increasing it through tail emissions.

If they form a fork that achieves the heaviest Bitcoin chain in terms of PoW, then Bitcoin will no longer have a fixed supply.

This is quite unlikely, but not impossible. If Bitcoin had achieved "absolute scarcity" it would be impossible. Therefore absolute scarcity is not a feature of Bitcoin, highly probable scarcity has been achieved at best.