Shoemaker-Levy 9 in 1994 was on a collision course with Earth, if Jupiter had not been in the way? I’ve not seen that stated anywhere. Do you have a (reputable) link?
Googling this, I found a couple (rather shaky) sources indicating that a collision with Earth was possible somewhere down the line, but those were initial calculations and were revised once Shoemaker-Levy 9’s orbit was better known. Granted, who would take Jupiter out of the equation?
I’d also clarify: MOST of the cratering of the Moon, as Earth’s, occurred in it’s early days, but not all of it. However, it is probably correct to say that the Earth protects the Moon more than the Moon protects the Earth (until we build an asteroid defense station on the Moon, anyway!)
The info on Shoemaker 9 I saw on The Science Channel, if they’re correct in what they said. What sources were you looking at? Face it, without big brother Jupiter out there it’s likely we wouldn’t be here. However the Big Guy can’t catch them all and one day it’s going to be POW!, Goodnight Irene! If the cratering of the Moon didn’t all occur in it’s formation then when did the rest of it? And when has the Moon ever acted as a cosmic shortstop, I’m curious to know? Mercury shows evidence of heavy bombardment as well as Jupiter’s moons Ganymede and Callisto. Because Europa’s surface, if not the entire moon itself is one big ice ball, it’s surface shows less evidence of cratering but only because the surface keeps freezing and then cracking apart.