> Nobody is claiming that any single tool - much less Duolingo - will make you proficient in a language.

Lots seem to have that belief, though. As I said in another comment, it's something you can see quite often in various language learning forums in Reddit (/r/duolingo) and Facebook, as well as on the DL forums themselves.

> If Dolingo is claiming this, that would be false advertisement / scamming.

They might not explicitly claim it, but they certainly imply it in my opinion.