I think it should match the art, because the art is there to add flavor, as does the flavor text. We're adding these to add flavor. So if there's a flavor mismatch, it's sorta weird. Plus, in some cases from the articles, the flavor doesn't describe the card, and they just made a word in a sentence hover to make the story/world feel more filled in than describe the card with flavor.
On the reddit comment one, it is sort of reaching to an extent, though there are a couple others that are reddit comments that fit better. I felt Passage of Eons as an example fit fairly well.
Another opinion to add: I think we should avoid adding too much text to the spoiler text box. More than 4 or 5 lines is too much maybe, though I think exceptions can be made for really simple or vanilla cards, because those always had more flavor text in MTG. Like someone posted the entire Dizo monologue a while back and that was fairly long.
On Oasis Sanctuary: Really cool flavor text, it makes sense.