Creating unique RPG Engine. How do I solve this problem?

I should return to what I was doing a few days ago, because everything I've worked on in the past day and a half is too similar to AD&D. I want my game to be as unique as possible. I also really want all dice rolls to use 1d6, 2d6, and at most 3d6. Mostly 2d6 should be used for all skill and attributes rolls.

Day before yesterday, I made a mistake. I started thinking that predefining character classes would make it easier to design the game and easier for players to learn it. This lead me astray, because I started doing shit too similar to AD&D. Some other traps include:

West End P&P engine

Battletech engine

Shadow Run engine

Hero Quest engine

Dragon Strike engine

I would like to figure out a way to pre-define classes without the game engine ending up being a rip-off of any of those systems above.

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I've also come to realize "mass damage" spells and abilities almost never add anything beneficial to the game. If the spells and abilities only have one target, the player is forced to make a decision about what really matters. If the spells and abilities "blow up the world" in one or two hits, nothing matters anymore and the game sucks. (Chrono Trigger or Final Fantasy with a high level character)
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I'm having a problem in that even with keeping it as simple as 1d6 to 3d6 for rolls, most players might find my game frustrating. It seems no matter what I do with this system, many people might need a pocket calculator to calculate stats and damage, which wasn't my intention at all.
Creating unique RPG Engine. How do I solve this problem?
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