Great post, GF!
I was simply wondering if he'd changed the style of his songwriting to accentuate the main melody as the hook, rather than the soaring falsetto hooks that were independent of the rest of the vocal stack-- almost a counterpoint, although I know it's not the strict definition of the term. I would guess (after a very cursory review of a few albums' tracklists) that "Getcha Back" is one of the last examples of that use of falsetto in a BW song. For whatever reason, he just stopped writing that way.
Interesting take, and you captured exactly what I mean when I talk about Brian's falsetto. Yes, I mean it in the general sense, but I mostly mean the parts you describe as soaring hooks (often wordless) that are independent of the rest of the stack. Those kill me every time I hear them. So yeah, he gets into the high registers in "Our Special Love"-- which is great-- but my larger lament is the notable lack of those sweeping falsetto hooks in Brian's recent work. There's a really decent one in "Kiss the Girl," but that's about it. I was hoping to hear some on this album. So far we're striking out.