Well, take a look at a 17th level assassination rogue. Attacking a creature during a surprise round, he benefits from both level 3 Assassinate and level 16 Death Strike. With Dex 20 and no magic weapons, using one short sword, he can pull 47 damage with a single attack against a surprised opponent, and double that in a failed Con save. If I counted it right, the later is enough to kill 111 of those monsters, including the lich, the vampire and the death knight, which are all out of range for the single 9th level spell, and here we have a 17th level character without a single ring of protection to call his own.
Everybody remembers the mage that wiped the army of orcs with a single meteor swarm, but nobody seems to remember the rogue that sneaked into the castle with +15 stealth and killed the villain with a single strike. At least with the mage you get to be in the scene when it happens. You know how many times a rogue can pull that? Not once per day, but once per fight, all he needs is a surprised opponent!
Do you think I'm worried about that? I'm not, because it's a 17th level PC! If each level corresponded to 5% of the challenges of the game, I believe a 17th character only needs to be fair to 20% of the challenges in the game, and should in fact be unfair to the other 80%. A mage can wipe an army with meteor swarm? Cool, evokers are all about battlefield control, a 17th level one should be able to control a small army. Assassination rogues are about backstabing things? A 17th level one should be able to one-hit kill most creatures in the game. I don't believe that's unfair, I believe that's what high level characters are supposed to do.
Cheers,