I'm at thousands of cards my main Anki deck. Since starting it, I added 10 new cards most days. My daily reviews are usually around 100. Granted it's a vocabulary deck for language learning so I just pass most cards in a few seconds based on knowing the word. For fields/types of cards that take longer I'd suggest scaling down the new cards per day accordingly.

There are definitely many things that Anki is _not_ good for. But for the things where it's good, there's nothing else like it. The UI might be stale, but this is outweighed by the add-on ecosystem.