I amnot contradicting myself. Thief is really weak. Copperfield is way too strong. It turns the game into a hot potato match of who can steal everyones copperfeilds.
My last try to argue with you about this. Imagine the following scenario: All Engine pieces around in sufficient quality, including a decent trasher. You start with 2 Copperfields, I have none. How often do you think you are you winning when you go for those extra-VPs?
I'll come in to offer a second opinion: Imagine a game without Copper trashing. Then, your thief luckily stealing my copperfield is at 12-point swing in your favor. Even if I get 5 provinces, you can still tie me by only having to buy 3 provinces. That's too big of a swing to be down to your good luck with your Thief. If this was a rare scenario, it wouldn't be bad, but there are probably as many games without good copper trashing as there are with good copper trashing.
Thank you very much for your input, it is much appreciated.
Copper trashing doesn't have to be good, if you want to avoid the "Copperfield battle". I just very quickly counted the number of cards that allow trashing Coppers (or Copperfields) on the Wiki page. I counted 59. I likely missed some, or counted some twice. On the other hand, I didn't include Landscape cards and I didn't include other cards that can get rid of Coppers or Copperfield (e.g. Island, Miser, Exiling cards) or hide them (e.g. Crypt, Haven and the like). Anyway, even only 59 would mean that 82% of Kingdoms have a possibility to avoid this scenario, and it is probably higher. Then, in the other cases, and on top of that, assuming that one player is really lucky, and even ignoring the fact that the other player can still get Copperfields back, the one with the Copperfields has two more junk cards in their deck. So even then, it is not a clear cut. Anyway, a valuable point one can think about, and to be sure about the numbers I threw in here, I have to look to the trashing cards more carefully. Thanks.
Edit: I forgot to mention: Before I posted Thief with Copperfield as Heirloom, I created 20 Kingdoms with a set generator (Thief always being in the Kingdom of course; and with the starting Copperfield in mind). On my level of understanding Dominion boards I found that 5 of them were clearly in favour of going for Thief+, 5 were clearly not, and for the remaining 10, it was difficult to decide. In my opinion clearly what you want from a card (design wise).