We're working on balance at the moment in preparation for 1.0, but those minibosses are supposed to be an extra-hard challenge that will kill a lot of first-timers, yeah. The idea being that this introduces a dangerous element that you can experiment with in safety if you so desire (they are quite beatable with experience), but also introduces you to the idea that sometimes you'll come up against a seemingly impossible challenge and you'll want to come back later once you've prepared properly.
Welcome to the forums, by the way!