Well, I'm sorry to tell you that you are just plain wrong with this statement. I've had my zagg on for months with the leather case and it does NOT come into contact with the case, much less push the edges up. Before the zagg I used several other e2e's including the orzly, the thanotec, and at least 2 others that I forget the names of and ALL of them worked with the leather case.
Spigen cases are notorious for not working well with e2e screen protectors, the spigens wrap further around the edge than many other cases. You can't use your experience with 1 single screen protector and case combo and extend it to anything else, all combinations are different. You're just going to have to trust me when I say that the zagg and the apple case work perfectly well together.