W.r.t data entry I've resorted at times to using a Google spreadsheet with autogenerated row UUIDs (it's useful for content to have a persistent ID in case you have to correct a typo or add new fields).

I also often found myself wanting to make different flashcard decks from the same basic information (for Mandarin pinyin sentence --> character recognition, characters --> English translation).

If there was a sheets like data entry interface backed by a text format it would be great.l (I rolled things with streamlit but it's always cumbersome to get started).

Yes, the inability to edit cards due to the content-addressing seems like a majot drawback.