Yeah, you're talking about something really important when it comes to talk about powers of cards. A game is indeed divided into three parts, like people on the net talking about RTS are used to talk about "thirds" of a game, like there is a game beggining, an expansion an a conclusion. Same for Spectromancer, on first third you play mana boosts (Priest of fire, Merfolk Elder, Elf hermit) and low cost creatures to wait to know more about the opponent's cards and strategy, and on the last two thirds you play more decisive cards.
So as you're talking about "overshadowing", it means that Bargul and Troll are in between two thirds. They're too expansive for first third, and definitely not good enough for second or last third of a game, overshadowed by more useful cards.
I agree too on the fact that more HP would not improve these cards, and they need another ability. Bargul could get a "frenzy" ability, every time he damages a creature he gets a +2 attack bonus.