Me? Haven't payed a dime, can kill most champions without spells and the rest with. Equipment you find suffices against almost every enemy you find (again, spells for the rest).
Also had invaders with levels lower than mine on a regular basis since the game can put you up against invaders up to 5 levels above or below your own.

While I do respect your opinion I have to tell you that you are misinformed and your conclusion doesn't reflect the reality of the game. I know at least one top leaderboard player that hasn't payed anything either. And from experience, that does mean he worked pretty hard to get there.

Facts. Get them straight.