But other coins can have unique qualities that Bitcoin can never adopt.
One such quality is simplicity. Although Bitcoin may be far less complex than some other chain like Ethereum, it still contains a nontrivial amount of complexity in itself, as witnessed by
Is there even a cryptocurrency outside of stablecoins(some even debate that it's not a "cryptocurrency") that is simpler than Bitcoin? I don't think it gets any simpler than this.
Another such quality is fair distribution. While Bitcoin had a relatively fair one, with no premine, it still did not decentralize wealth as much as one might like. Or rather, as future generations might like, since each successive generation only gets to mine 1/32 time as much as the previous one.
I don't think decentralizing wealth was the plan nor is possible in the first place. The most we can have is equal opportunity; fair distribution of wealth is a pipe dream.