Greenies didn't give anywhere near the advantage of steroids.
They enabled players with skills to be able to perform those skills when they were tired or hungover. A light hitting middle infielder with warning track power wasn't going to start hitting balls over the fence due to amphetamines. A pitcher throwing 88 mph wasn't going to start throwing 92-93 while on speed. Players definitely benefitted, but they had to have the skill set to get to the league and to perform in order to realize those benefits.
Think about all the fly balls we see every year that are caught at the warning track. Many of those turned into home runs because players were carrying more muscle than their bodies could've naturally produced. Higher exit velocities from stronger players turned some singles into doubles, ground ball outs into base hits, etc. Players who may not have made it to the big leagues on their natural abilities were able to do so while juiced.
The only real similarity between the two substances was the enhanced recovery times from injuries with steroids, versus the recovery from fatigue or hangovers with amphetamines.