Another example to illustrate why we need the ability to flag/tag notes AND cards: actually, if you have several cards made from a single cloze note:
Some {{c1::days}} I feel like a {{c2::leprechaun}} at the end
{{c3::On other days}} I feel like the one in search for the {{c4::gold}} at the beginning.
…and card 1 gets automatically tagged as a leech, all four cards from that note will get tagged as leeches no matter how easy they actually are, which in my opinion is neither expected nor desirable behaviour.