I play big decks most often (though I’m not A20, I think I have defect around A10?). I don’t go for the Heart usually unless it happens to line up with my strategy and then why not? I personally feel going for the Heart is a lot more luck dependent. But don’t feel that way at all about beating the Act 3 bosses. I believe this is why ascension levels only depend on beating the Act 3 boss. The Heart is just a bonus crazy challenge. I personally assess how well something works based on its ability to get me through Act 3.
I find big decks work pretty well with some luck mitigation. There’s still going to be luck because it’s a card game after all. The Watcher has a lot of extra card draw and scrying to mitigate luck. The Defect can build baseline guaranteed defense with frost. The Ironclad heals after battle so can take a few surprise hits. He also has a bunch of ways to carry-over block. I have no idea how to play the Silent big deck style though.