Incorrect. First you play out all the costs, so discard the Just a Nuisance, however you play response to it, to put it on Treebeard instead, then you play out the effect of removing an Uruk-hai, however due to bibfortuna's interpretation, the effect doesn't take place, since you failed to pay the cost.
(You may disagree, but I'm not incorrect. I'd say you're incorrect, too, but I know it's just a matter of perspective because the rules are NOT crystal clear. Anyway,) if you didn't pay that cost, you wouldn't be able to use
Earthborn's effect. Also, you said it yourself that "first you pay all the costs". I ALREADY payed the cost, THEN I played a response. Again, if the cost hasn't been payed, the response wouldn't activate, would it?
And no, your logic doesn't work, if you had a card: "exert a companion to remove a burden", if you choose to play it, and there is no burdens, you still exerted the companion, even though you didn't remove a burden.
I also disagree. You did the action of removing a burden, even though there wasn't any. It's like making your character drink a Potion while his HP was full. You'll even see that he restored 100 HP because of the green numbers, BUT he couldn't get more HP because he was at max. The potion is wasted, too. In other words, just because we didn't SEE the effect doesn't mean nothing happened at all. It's the rule of doing as much as you can and ignoring the rest. You didn't ignore because you failed to follow a rule, but the contrary.
Anyway, we shouldn't go thinking there's a right answer to these questions. This game has a lot of holes. But I agree with mardukra. It's like the previous discussion about SoS.
- Exerting pays the cost, but you don't place the token as an effect of SoS.
- Discarding
JaN pays the cost, but don't put
JaN in the discard pile, you stack it on
Earthborn.
Again, it's a matter of perspective. Does the "instead" on
Earthborn refers to "
stack instead of
discarding"? Or is it "stack it
here instead of the
discard pile"? While I think it's the latter, we'll never be 100% sure, even if we ask the original developers (even they might disagree). We could, though, get to a consensus.