Assuming they were actually keeping the contents of such wordlists out and actually ensuring high-entropy passphrases, we would be in an OK place, though still far removed from the security provided by randomly seeded ECC keypairs.

I'm fairly skeptical of the ability of software to "ensure high-entropy passphrases". I don't think it's trivial to anticipate the entropy-lowering strategies that people will come up with in order to help them remember their passwords.