Here is how I look at your question.
An LS7 in a 1LE would maybe be equal to a ZL1...........maybe. The 1LE is 150 pounds lighter (supercharger) and would be 80 HP down from the LSA. How does that car run with a ZL1? What you would have is just another version of the same performance. And simply putting the LS7 in the 1LE would give you a $50,000 car. So it would be the "lesser" of the two cars.
To give the Z28 a reason to be, beyond simply a badge, GM had go above the ZL1 in track performance. And to do that you get the LS7, the best brakes GM knows how to do and enough weight reduction to make up for the 80 hp.
Now in a straight line, a ZL1 might actually run faster than a Z28. We'll have to wait and see. To give the Z28 it's "reason for being" it needs to be lighter so it can turn in the corners better, accelerate out harder. That's the 300 pounds. And no one should assume that that was simply throwing parts out (like we've discussed over the past few years) It took real, honest to goodness engineering and testing and validation and I can assure that is NOT free or cheap. And to give it another advantage you add the best brakes known to passenger cardom. Combined with the LS7 you now have a NA engine with low mass and chassis and brakes to get this car to nearly Z06 levels.
I'll be very curious to see the tests.
Also keep in mind that since the ZL1 already beats the dead Boss and GT500 around the track, there is no real competition for the Z28. It stands alone as what it is, and how it goes about it.
I know everyone would have loved an LS7 in the 1LE. We had a thread on that well over a year ago. It just wouldn't have justified the car or the nameplate relative to the ZL1.