In roleplaying games, sometimes the characters who make up the adventuring party aren’t all at the same power level. In the olden days, that could be because a few characters died and had to start over at 1st level while the survivors were at 4th or higher, because one unlucky soul bore the brunt of the wight’s level draining, or because someone rolled a string of 18s during character creation. In newer editions, it tends to happen because a few players are experts at cramming every possible bit of destructive power into a character while others take a more casual approach, prefer to invest their points in something other than combat prowess, or simply don’t pay much attention to swords and arrows and other nasty things.
No matter what the cause, the result from the GM’s point of view is a group of characters that’s hard to challenge. While Grimjaw and Skullbuster are chopping monsters into coleslaw, Sunflower and Gigglebear are being pulled inside out and dropkicked back to the Bush administration.