Ideal vs. Compromise
I think it is reasonable for most people to expect a somewhat managed, not totally decentralized, and not totally immutable ledger. People’s priors are those of competing, centralized, managed and fully mutable ledgers. Those ledgers adapt their attributes to the demand of the market. Bitcoin represents the opposite polar, being fully decentralized, autonomously managed, and immutable. I believe Ethereum aims to be a compromise, and in that regard it has fared pretty well, gaining support from more traditional industries as a result.
You are right that Ethereum is not aiming for long term value preservation. I believe Vitalik has stated publicly that Ethereum is not the end of the progress, and he expects something better to replace it down the road. I am not even sure Vitalik means value preservation in terms of “progress”. Ethereum is a credible public computer, and Ether differs from Bitcoin mostly in that Ether has an actual use from the beginning: buying “gas” to drive the computer. Unlike Bitcoin facing competition from traditional payment services, Ethereum is creating a large community focusing on publicly credible computation. Bitcoin has to expand into a red ocean if it wants to be a well accepted payment method outside of black market; Ethereum has been expanding its blue ocean to all kinds of traditional industries. So even if Ethereum has less focus on long term value preservation, I believe it has a better growth potential, and a better mid term value.
In the end, I think trust can only rest in people in the long term. Laws are written in Congress. Evidences must be presented by a witness. It seems to me that Ethereum has a better story about collaboration within its core and cooperation outreach. To that end, the fact that it can be intervened by cooperation just in case may be a relief to most people. Therefore, I believe it would be more attractive than Bitcoin outside of the enthusiastic circle and black market.