The only thing those coins which promote themselves as “Ethereum Killer” will actually kill is your capital, investing in those coins is for the most part a bad idea, as they are just trying to hype their own coin by using the fame of another project.

And even if by some miracle those coins were any good that does not mean that whatever coin they are actually trying to replace will disappear, after all as long as a project is a good one there is a space for it in this market.