I don't follow altcoins at all, but it seems to me that Ethereum's main problem here was that its economy wasn't backed by very many full nodes at all. See:
https://en.bitcoin.it/wiki/Full_node#Economic_strengthhttps://bitcoin.org/en/bitcoin-core/features/validationI'd guess that 99% of ETH owners were using EWallets. This is extremely dangerous, since it gives those EWallets massive control over the network. This is exactly the sort of centralization risk that Bitcoin experts are constantly warning about in relation to the max block size. 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.