The change in swingweight is a direct result of the length removed from the shaft. If I follow you correctly, 1 1/2" has been removed from the shaft, net the clubs are now 3/4" shorter than the standard Titleist length.
Yes, that will reduce the swigweight. But the distance loss is tied to the clubs being shorter:If you hacked the five iron 3/4", it's now somewhere between a six and seven iron in length.
It could also be a terribly bad shaft match for you.
Tiitleist may be able to give you the build specs if you provide the serial numbers for the clubs.I can't recall if they will build to a longer length and a requested swingweight, or just accommodate changes in length. Big Stu might know,