VFR on top is a hybrid. You need an IFR clearance to get through the IMC and then maintain visual flight rules while you are conducting the operation. It has already been covered here that you can't get a VFR-on-top clearance in Class A, despite being IFR. Further information can be found in AIM 5-5-13.
It's defined as an IFR operation. The AIM isn't regulation or law, and this is one of the many cases where it oversteps and says something that isn't substantiated by law or reg.
If it was a VFR operation, you wouldn't be constricted to your route as you are with VFR-on-top. You're thinking about climbing and cancelling, as VFR-over-the-top, which is a VFR operation.
VFR-on-top only gives you altitude discretion, subject to VFR wx mins. Otherwise, to cite your beloved AIM:
5-5-13(a)2: (c) Comply with instrument flight rules that are applicable to this flight; i.e., minimum IFR altitudes, position reporting, radio communications, course to be flown, adherence to ATC clearance, etc.