Alot of your answer is going to depend on how you inerpret the question. If it is for a single at bat, perhaps you could throw Pedro in there.
If I were a player, and I saw Pedro's name as the SP, I'd figure I'll get maybe 2-3 at bats against Pedro before they pull him and hand it over to the bullpen. Try to work his pitch count up and hope he goes away.
If I saw a guy like Johnson a couple years ago, I'd think Oh damn! I might have to face this guy 4 times! a 6-10 monster with a nasty fastball. A guy like Gibson, if I was lucky enough to hit a HR off of, I'd be even more more scared to face him the next time I got up to bat. I'd put both of them ahead of Pedro.
If Pedro can overcome his injury history and string together a few healthy seasons, roll up a few more CGSO's a season in that span, and put the whiner label behind him, sure he could be considered one of the most dominant ever. Right now, I think his injury history lowers his intimidation level, and he is likely viewed by many players as a guy you can rattle emotionally.
* Steroid induced record