I don't want to say your wrong about your own experience, but I think sometimes SRS can subjectively feel very unproductive even when it's working great because of the way it constantly surfaces material at the edge of your knowledge. It doesn't often give you the satisfaction of smashing through a series of problems you can answer easily. If it did, it would be wasting your time.

I also think there is a real skill to formulating good flash cards when using SRS that I for one don't think I've yet mastered.

There seems to be a lot of research about SRS but I never see any research about what makes an effective SRS flash card. Maybe it’s different for every person and/or subject. My foreign language skills improved considerably once I stopped putting english on my cards at all and used only the target language + pictures. But, like the person you replied to, using Anki for anything other than language learning has been mostly a waste for me. I do suspect it’s more to do with the decks I’ve created than with the SRS process.

I don't use Anki, but I do use Space Repetition. I've explored different styles of stacks, and found that even for apparently identical underlying information, some formulations of that information work and are acquired easily, and other formulations simply don't work.

The underlying "atoms" you embody in the cards matter, and possibly matters a lot.

Would you mind posting some examples of the kind of cards you have in Anki?

I've experimented with a wealth of homemade and premade decks.

A lot of vocabulary decks based on textbooks used in class, e.g.:

    人 -> person

But I find that for more complex words, I reconize them in Anki, but not in texts.

I also did a large premade deck of example sentences from a grammar book, which I actually found to be very helpful for general language understanding.

I've also failed trying to complete Heisig's Remembering the Kanji, using Anki.

What worked best for me was putting in sentences rather than single words.

So I might put in: ハンバーガーを食べる

Then there's two good ways to practice this. One is just reading/recognition. Can you understand the sentence?

The other way is to make it into a card to practise output: ハンバーガーを_____ (eat)

The part in brackets is a hint to help you get the correct word. Your hints at the start will often be direct translations of words, but you can also use images, emoji, dictionary definitions in the L2. Anything is ok, or combinations.

I often make my output cards very easy:

ハンバーガーをた____ (eat)

While it may look too easy, I still have to remember the word I'm studying.

In general words taken from real books, TV shows, youtube videos tend to stick in my mind a lot better than words from textbooks, wordlists and grammar books. Those tools have their place but they're not the be all and end all.

Good luck! And remember it's a long road. I've made 6000 flashcards over 10 years to learn a second language and I'm still far from "done".

Have you tried using Wanikani? I have been using it for less than half a year and I already know more than 600 Kanji, most of which I can recognise in written text also. Of course, it helps if you reinforce the material through some other means, too, e.g. by working through a textbook.

disclaimer: not affiliated, and WK is not a perfect product (they have some weird quirks), but I've found it to be rather effective. You can also the first three levels for free.

I think this realization is one of the most helpful parts of Anki. Remembering stuff is always harder than we think it is, SRS forces you to face that fact head-on. It doesn’t mean “don’t use SRS”, I think SRS is still worthwhile, it just means you have to be more intentional about what you decide to commit to memory.

Personally, after 10+ years of consistent SRS, I focus only on vocabulary/terminology and fundamentals. Trivia is never worth it.