bitcoin gives a proves in some country, and you can see that there are ATMs installed in that country so people can use the machine.
Except bitcoins, most other coins are just the existing and simply following bitcoin for having real-life applications. Simply we can say they are all just here for no reasons in the view of a payment processor. ATMS are not an innovation of cryptocurrencies and BTMs are being installed for the reason providing people easy access to cryptos.
But at least, other coins have benefits too because, with those coins, I am sure that it's a way for us to earn more bitcoin and then we can use bitcoin in our daily life. Although the altcoin is not like bitcoin, the existing of the altcoin are help bitcoins too and make cryptocurrency grows.
Besides that, we can use bitcoin as another payment system by using the third party, so we don't need to confuse about converting from fiat to bitcoin because they already calculate the converting.
Bitcoin is itself a payment process on its own but we need third party support when we do think about converting it into fiats to escape from price fluctuations. This can be a case against any altcoins too as altcoins are also heavily fluctuating.
Yes, we still need the third party to help us to convert bitcoin into fiat, but I am sure that when bitcoin can grow, we don't need third party and bitcoin can be used as fiat itself. We can see in the future, many people use bitcoin as a payment process, and they have another new type for the payment.