There are lot of crypto currencies that were created to compete with BTC
BTC lightning network is implementing due to the scalability issues the chain is experiencing with high 'fees' and transfer times..
If lightning network is implemented in Bitcoin will it destroys these competitors?
I do not think so.
It seems to me that the cost of a transaction is not the main one when choosing a cryptocurrency.
Bitcoin Gold has free transfers, but this didnt destroy all the altcoins and bitcoin.
I'm sure that in the future there will be more and more new altcoins.