One particular area where I get the impression they have a specific measurable impact is in their legal support on certain cases:
https://www.eff.org/legal-victories
Then there is (for example) their practical solution of how to help increase HTTPS adoption with their excellent software tool, CertBot, which helps automate LetsEncrypt certificates:
I’d note that it seems to be exceptionally rare for a politically active organisation to be able to both campaign on issues at a high level AND produce technically viable and relevant software tools. Those are two wildly different areas of expertise, and yet they do this, with a clear overarching narrative.
In terms of proposing more specific solutions to problems they protest against, I don’t have a strong view on whether you’re right to emphasise this or not. Maybe there is more they could do here. But in terms of the larger question of “are EFF effective?” I’d say they are demonstrably having a positive impact.
Is it enough? I don’t know. How do you measure it… Can they do better? Almost certainly.