Even though the 3-4 defense has changed over the course of the past several decades with teams now primarily playing in nickel or even dime defenses, the general understanding of the alignment is that, like the 4-3 defensive end, it is the outside linebackers around which the formation is built, setting them up as the playmakers, particularly as pass-rushers.
The Pittsburgh Steelers have had a lot of great pass-rushers and some high-quality tandems over the years. The run that James Harrison and LaMarr Woodley had in the late 2000s and early 2010s may have been their very best.