But you're thinking of it as getting a ruin compared to getting nothing.
I think +1 Card, and even +1 Action are both better than a truly blank card (or a Curse or an Estate).
So maybe the rule for Ruins is more utility than a curse, less utility than a card you would spend money on.
IMO, +1 Action is just barely better than a blank card. It is only better in edge cases -- TR, KC, Conspirator, HoP, etc. Otherwise, it is functionally equivalent to a Confusion. You might as well not be able to play it.
+1 Card is better than +1 Action in that, if you have an extra Action at the end, you can play it and get the next card. It eats an action, sure, but it still hurts less than a Confusion that just takes up room.
+$1 is similar in that it eats your action in exchange for a Copper.
+1 Buy gives something potentially useful as well.
+1 Action is the worst one in almost all cases and would basically be a Confusion card.