I am not as expert as any other steemian replied, but this what I feel :
ETH is project it had a start & certainly it will have an end; however new ETH based projects will continue to pop up and that will make ETH survive for more. Bitcoin is a CONCEPT that make the VALUE.
Competitors are two types; 1st. is Projects that based on other platforms like PIVX & Zcoin; those projects will make more room for ETH to fight back for survival; the 2nd. type is Ponzi ICOs that have nothing but a name and business, this type dies faster leaving ETH & competitors.
As long as Bitcoin keeps both value and concept; ETH will keep the value if developers keep the platform more morphogenic to overcome new features that competitors offer.
I wish I made my point clear :)