Steyn's peak performance was around 2010 vs India in India. That's what I'll be remembering him for.
Steyn was a beast. But he was hardly alone in being peerless in his generation. Between 2000 and 2007 McGrath was miles ahead of his contemporaries and in the best era for batting by far. 14 out of 42 batmen in history who averaged 50 or more played during that era. Rabada has played 32 tests now and has a lower average than Steyn. McGrath played 124 tests and has a lower average than Steyn. In between these two Steyn was the best in the world by a long way. There other sub-25 average bowlers who had careers simultaneously with Steyn - Philander, Harris, Pollock, Bond, Abbott, Clark and Asif. For one reason or another none of them played right the way throughout Steyn's career (Pollock due to age, Bond and Harris due to injury, Abbott due to quotas, Clark due to form, Asif due to cheating) but Steyn was hardly alone averaging low 20s during his career.
Interestingly enough, McGrath wasn't peerless during his 2002-2007 reign. Bond, Clark, Akhtar and Asif all had sub-25 averages and >50 wickets taken during this era.
I guess the point is that there is no such thing as a peerless player. Steyn ruled the roost and was the best bowler in the world from 2007-2013ish, but he's not been the first "best bowler in the world" to have happened.