I have a small concern regarding HP.
Remember these Firebolt OTK decks? Well, these makes all fights until like Level 30+ incredibly easy due to the very low HP nature of NPCs. I tried out this mode in trainer without any cheats, and was able to get an upgraded card far earlier than even getting my rare (score 138), using the fire starter deck for the sole purpose of getting the bolts, immolations, fire pillars, etc. I didn't bother putting that much thought into the deck, but it does work. Granted - new players probably aren't that savvy, but my point is that I guess getting upgraded cards wasn't intended to be *that* easy.
Also managed to win 5 upgraded fire lances from a single win against Pyromaster (who is incredibly easy to counter even for a starter - a single reflective shield is an autowin) :p