There is a large amount of randomness to the game. Sure some random events are more powerful than others, and surely SGLs are the most powerful. But they are also quite rare. Maybe not rare enough for non-Scientific civs. Perhaps it should be 1% for them instead of 3%. But 5% for the Scientific civs is acceptable to me. Otherwise the trait would be sub-par, just as removing an increased chance for leaders for Militaristic civs would make it subpar. Removing the free cities for Expansionists would make it the worst trait in the game (if it isn't already.) To the above poster who quit upon rushing the Pyramids, would you quit if you got a free city? Would you quit if you got a military leader on turn 15?
Yeah, you might pop a SGL from The Wheel or something every once in a while - maybe a handful of times in your entire Civ "career". But the fact remains that they are rare, and that all civs have an equal chance to get one, among their group (i.e. Scientific and non-Scientific.) I didn't mean to imply in my post that popping a SGL is always the result of planning and effort. But you always know it's a possibility, so you can try for it or not. If you pop one without trying, then you really got lucky. If you try for one, and pop one, you still got lucky.
I guess what I'm saying is, nearly every aspect of the game contains an element of luck, from your starting terrain, to the resources nearby, to your neighboring civs, to your success in battle, and on and on. The combination of the luck factor on SGLs combined with the power of the Pyramids is probably too much. But the fact remains it is a rare event - increasingly so as you move up difficulty levels, since the likelihood of their being completed prior to your SGL goes up. Is an event that happens one in 100 games really that overpowered?