A bit of a necro, but it's not that there's a lot of discussion on this forum anyway, right?
What i read here is that plenty of people very underestimate the tempo difference between player and enemy, which is very crucial to analyze power of SoB.
Yes, on paper most of the time both players get the same number of cards and very often player casting SoB actually gets less cards than their opponent, but there's the trick - player using this card has first opportunity to use these 3 cards. It's a big deal when you consider that in these 3 cards you can draw that vital kill card or piece of combo or disruption needed to stop your opponent. In these situations it does not even matter that opponent draws cards because they can simply never live to their turn, or get into position where these new 3 cards are useless.
Purely number wise SoB is fair for both players but if you consider how big of a tempo swing for caster it may be, there's point to be made about it being extremely powerful card.