Anki does scale. It won’t ask a new user to review too many cards per day. As cards are memorized the increasingly spaced intervals make room for new cards. So

Anki does scale. It won’t ask a new user to review too many cards per day. As cards are memorized the increasingly spaced intervals make room for new cards. So if you dump a thousand cards in at once, which you shouldn’t do, you’ll be directed to load them into the memorization process over several weeks of daily reviewing. Agree that most notes from other documents don’t make good cards. Making your own cards is worth the time spent, for the most part, although there are plenty of standard decks you might as well clone (Greek letters, as a simple example.)