Ethereum is not going to be the 'blockchain to rule them all'. Saying ETH will fail because there are other *untested* players in the game is shortsighted in my opinion. I see a polychain future, ruled by no single blockchain. 
You are seemingly blinded by the hype around EOS. Competition is good but these projects are not necessarily direct competitors. 

>as new competing projects with more competent developers show up, these projects will put the nail in Ether's coffin. I will name two projects, Qtum and EOS.

Competent developers? Those aren't working on ETH? Nail in coffin? What coffin? - To be serious, there is a place in the market for EOS and Qtum just like there is a place for ETH. Each project is unique in its approach to applications and consensus; tradeoffs are made for each project. Each project will have users whom want the particular tradeoffs granted by the platform. EOS won't take everyone from ETH, nor will Qtum. Both will share part of the pie.