Systems where character power scales exponentially?

Sometimes I run campaigns with a superhero theme and I want the player characters to be more powerful than novices but to start so far below the most powerful villains that they don't pick suicidal fights. I'm looking for a system that scales character power into tiers such that middle tier should never win fights against top tier, but has a chance to beat the tier or two above them. I want something that would give the players a reasonable idea of how risky an enemy is without relying on my narration to fully convey it.

In dice-pool systems like Vampire the Masquerade, rolling 10d10 as an elder isn't much more impressive than 7d10 as a middling vampire. In Dungeons and Dragons, if novice PC rolls natural 20 and elder boss rolls a 5 the novice wins.

The closest I've encountered to dramatic power scaling is when ship-scale weapons hit human-scale targets in Star Wars the damage is multiplied by 10 (or divided by 10 in the reverse).