It's weird to me for "ease factor" to be an intrinsic property of a card/thing to learn at all. I study things like Chinese characters with Anki and it's not but just rote memorization, there are systems and structures of knowledge for each card's content to be integrated into. For Chinese characters (as with many other things) there's history, etymology, deconstruction into components, personal mnemonics and associations, literary context and references, etc., all of which affects how easy it is for me to learn any one card's content. Usually i do not initially know much for a given card, but other cards and external learning will make any given card easier over time than it initially was.

And the set of external factors for any card is not fixed; there's no "true ease factor" for a card, because the set of external factors i will probably encounter is not a fixed (determinism aside) property of a card. It depends on me and my changing state.

I assume this is about Anki, but even for archive it goes to 404 for me.

I can access it without issue.