Well, a fixed supply yields better monetary properties, which people are likely to value. I don't really think a cryptocurrency can win in the transaction nich

Well, a fixed supply yields better monetary properties, which people are likely to value. I don't really think a cryptocurrency can win in the transaction niche without also winning in the store of value niche. I think it's a winner take all situation. As a separate point, I don't know if Ethereum or Polkadot really can scale to meet the world's needs (I'm skeptical), but any cryptocurrency can scale arbitrarily if you use offchain intermediaries (e.g. like PayPal) for small transactions.