Mental notes < written notes < SRS < repeated exposure + emotional connection.
Specifically around retention (and only retention), taking notes doesn't get you everything, but it gets you something.
(I do feel some of us put undue focus on taking notes at the expense of understanding the world through empirical means, but that's another discussion. I'm focusing solely on retention here.).
Active recall testing and distributed practice are great ideas. No disagreement there. (the Ebbinghaus curve is well known)
(also, thanks for the link to the publication -- those are interesting results that describe aggregate outcomes for the population studied, but there's usually variation in individual outcomes, and in self-selected groups like this one, a different subset of techniques may dominate)
To your point about Anki specifically, I'm a language learner and in my experience, flashcard-style SRS can help retention for atomic types of knowledge, but I find as I get to intermediate levels of a language, the utility of flashcards declines precipitously -- because one is called upon to synthesize structures rather than just words.
So far I haven't found an easy way to encode structures into flashcards (clozes etc are too simplistic)... furthermore, language learning is complicated by the need to acquire a "feeling" for the context of how certain words are used. It's a kind of tacit knowledge that sometimes defies simple flashcard-type encodings. You can encode context through narrative, but then your flashcards become too unwieldy.
I've found writing and speaking (with feedback) in small chunks over a long period of time to be much better at creating the "neurocircuitry" necessary for retention. Again, I wouldn't say flashcard SRS are bad at improving retention (I use them), but like taking notes, even if they don't get you all the way there, they get you somewhere.