I also don't believe they can mess with ethereum and it's impossible to kill him again.
People will also think first when there is a new network that is present, even if they install a cheap price, they will also think if they want to use it.
"Kill him again"? So, you're saying that eth have died before due to other altcoins? Hhmm but what I know is that eth have rank down from the second spot to 3rd, and I think bnb was the coin that kicked eth but luckily eth reclaimed its spot later on.
Many alts can mess up with eth because they can provide solutions from the known issues eth is experiencing now but that's the only thing they can do. Eth is still more secure on them and has other advantages which is why it cant be totally killed. Once the eth 2.0 is complete this can make the coin strong again. I bet devs of other networks are now threatened as they know that their end is near.