I also think that this economy could subsist perfectly with a few cryptocurrencies, which in practice is happening tacitly: it is enough to check coinmarketcap to realize that only the first 10 cryptos occupy 90% of capitalization, while all the others have to subsist with only 10%.

Now, we must be aware that the vast majority of these listed altcoins are not true coins, but tokens, and in that case many of them do have a justification to be created to solve a problem or for a practical and very specific use.