Ok, so your argument rests on this foundation: Events are the same as Event cards, and so whenever it says "Event", it's short for Event card (like Treasure or Attack). So you actually claim that we buy Event cards, but Event cards are not considered cards. I'm sorry, but this is pretty weird. A card is actually a physical component that you can buy and gain in Dominion, this is why buying an Event is not buying a card, because you can't actually buy that card. You say "Event card" is just a name, like "Fool's Gold". But "Event card" is clearly not a name (except for the "Event" part), it's called that because it's an actual card! Do you really think it's just a coincidence that Donald chose to call it Event
card and it also happens to be a card physically speaking? A Coin token is called that, but it's because it's physically a token, so when Possession mentions tokens, Coin tokens are included. By the same token :p Event cards are physical cards, but the cost stated on them is not the cost of buying the actual card (since, you know, you can't), but rather the cost of buying the Event it describes.
Note that nowhere do the rules ever talk about
buying an Event card. Event cards are only mentioned as something that is included in the game and can be shuffled during setup.
You claim that you don't buy this weird event card thing, but buy the Event itself. It follows that the Event card is not the thing that has a cost printed on it.
No, that doesn't follow at all. Costs of things you can buy can be printed on all kinds of game components: game boards, player aids, cards, tiles, even rulebooks. It's just that for Events in Dominion, the cost and the thing you get are both printed on the same card. That's not disputable. The thing you get is not that card. That's not disputable either.