Armor in warframe actually doesn't give diminishing returns. The first point of armor gives the same amount of effective health as the thousandth.
The problem with this game is damage seems to be rounded down, or to the nearest, and not up. Taking attacks should always cost HP.
That and Gross Eater is flat out over powered. Can eat weapons, spells, and even players for a one hit kill, with no mana cost and no cooldown.