I do not see how you can make that assumption and project what you would do onto others.
I would use the FP+ right away at a headliner to avoid the SB line that builds at RD and then I would hit some other less popular attractions.
I think it all depends on the park on whether as many people will still be there at RD. i could see less people at HS and Epcot because of this but not at the other parks.
Admittedly this is just IMHO of what most would do, there will always be outliers and those that fall outside the standard deviation . Also, it is not a projection of what I would do, as what I would do is take another FP+ option instead of a first thing headliner.
My opinion is based upon my time as a park cast member, having many friends who were/are also park cast members, my observations as a yearly pass holder for 6 years and my education in behavioral science. I could be wrong.... then again I may end up being right...