You shouldn’t say it like only a newb would love this game, I still think it’s great - it’s just that its formula means eventual mastery (until they release additional characters).
Anyway, some bosses are clearly supposed to go against specific decks. That automaton with sentries works against small decks, I think, which otherwise may be great. They allow you to get most of your deck on any given turn so you know you’ll get what you need when you need it. You can still block this kind of damage in a variety of ways. There’s a status effect that reduces all damage to 1 or some relics make you ignore first damage - you can get it from potion or some talents. You can add a lot of armor with combos, but it’s more viable for Defect or Silent than Ironclad which you’re probably playing.
Also be sure to Weaken that dude. And - yeah, you’ll probably have to eat some damage, but you’re always healed after the boss so sustain is not that big of an issue. It’s unlikely he will shoot this thing more than twice during combat.