it seems to me that Ethereum's main problem here was that its economy wasn't backed by very many full nodes at all.
I was always under the impression that (possibly until recently) the only wallet software available was a full node. Although I suspect that a lot of etherum was stored on exchanges considering trading volumes.
It is absolutely essential that the economy be backed by many independent full nodes so that miners + a small handful of "major players" can't completely change the currency.
What would you consider to be part of the economy that should be backed by a full node?
Someone who is interested in Bitcoin but never owns any, even temporarily? - No. (this person running a full node might be helpful in terms of hosting historical blockchain data).
Someone who buys bitcoin on Localbitcoins (or another exchange), and the withdraws bitcoin to their wallet?
Someone who buys and sells things on a peer-to-peer basis in the marketplace sections of the forum - with reputation that results in them sending first?
Someone who buys and sells things on a peer-to-peer basis in the marketplace sections of the forum - with reputation that results in them sending last?
Someone who only buys things on a peer-to-peer basis?
Someone who buys things from larger businesses (eg someone who buys from gyft, Expedia, ect.)?
A small business that accepts bitcoin alongside fiat as a form of payment, and has a few hundred thousand to a few million dollars worth of bitcoin sales per year?
A major bitcoin related business? Yes (obviously)
A major bitcoin exchange? Yes (obviously)