Hehe you are right that Shiv strategies in particular are not amazing for Heart or Time eater for that matter, however this does not mean that its impossible. I have seen a few pro runs (jorbs and baalorlord are two good ones to watch if you ever want to improve skillset - although thats better done after you are stuck at some difficulty) that have demolished heart and time eater in some cases with insane shiv decks. Its not as common, but definitely doable with the right synergies. For me defect is the hardest class to play, making his early game insanely clunky if he doesn't find the right cards. Ironclad is not too bad once you realize the power of exhaustion. The games are quick you should indeed strive to raise the bar. :)

PS: In my opinion in this game you need to learn adaptability, no run is ever the same, and this will always mean making different choices, and we should never feel specific about going for a specific strrategy. should just focus on making a deck with good cards to win each act and problem. one at a time. The heart is optional you don't need to kill it on every run. Not all decks can beat it anyway.