I just compared my PF and SF with each other and have to agree, that SFs have a disadvantage in rebounding. MY SF has a 9 in rebounding, while my PF has a 7. Still, my PF makes five rebounds more than my SF, which is huge I think.
Both of them played the same position on defense and on offense by the way.
Yet, there are two things I would want to take into consideration. Firstly, my PF has +5 in experience, which has a decent impact on a players performance overall I think.
Secondly, many people like to play a 3-2 zone defense, which takes the SF further away from the basket, and, if one plays man to man defense it can be the same thing, if the opponent's SF is rather guard-like and shoots more from outside.