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?
Lightning cannot solve the problem, but is rather a way of postponing it. The problem with transactions is generally a problem of blockchain. Finding blocks becomes more difficult and time-consuming, and the more transactions occur (and that's a natural process of coin's adoption), the more expensive and long it takes to perform one. What can really be a game changer IMO is the DAG technology. It actually works in an opposite way with transactions getting verified faster and cheaper (when the price is even there) when more people are in the system. Why? Because all of the users give some of their computing power for this process, thus making it work and in a way paying for transactions.
Anyway, cheap transactions will not circle out even other blockchain cryptos, because it's not just about speed and price. Many projects are far more than a decentralized platform and they will leave as a way of monetizing some business. Moreover, bitcoin is simply not good enough for some things people already got used to. It's impossible to create smart contracts, lauch ICOs or create tokens.