It is indeed strong, but why do you think it's TOO strong, marsu?
The stats are already very good. I would kill for a 7/2 vanilla for 6
- and Life already has a bonus for creatures, in contrast to Light.
The effect on the other hand is ridicoulusly strong. If you played a mono Light with 6 of these vs a standard mono Aether with 6 Dims, you'd heal yourself for almost as much as the opponent could damage you per turn, not to speak of the fact that it's max HP and thus has an insane synergy with the in-element Miracle. Oh, and speaking of synergy, also Blessing.
In short, the effect is way to good for a creature who would still be useful if it was vanilla to have.
Your other question probably deserves a thread of its own, but in short: Each element having weaknesses and strengths, a character, a feeling - that's not a small part of why this game is so great. Take it away, and the enjoyment of this game suffers. I also don't really see your problem to be honest, because you can still have innovative stuff (see this creature's ability) or even abilities that don't directly fit a certain element, but have a fitting drawback (See the great 'Grateful Oak' for example).