"I see no practical way that using 4 piece rather than a 5 promotes creativity one way or the other."
I think you're looking at it wrong. It promotes creativity because - with fewer tools - you have to think more about those fewer tools and how to use them more creatively. If I play a very small venue where all I can bring is snare/hats/ride I have to be more creative in how I play and use those limited tools. Yeah with a bigger palette tons of drums you can be very creative, but when I take most of those tools away you have to be more creative with what you have left.
Well sure - if you define creativity solely as "coming up with ways to make do with limited resources, this is completely true. But I really doubt you or any one else thinks that creativity is limited to such a limited utility.
I've done performances with only a snare drum (the late Bulgarian pianist, Milcho Leviev asked me to do this a few times) and yes, it was very creative and challenging. But again, creativity isn't just about transversing limitations... effecting compromises. For me, it is far more about - coming up with the best solutions drumming-wise for the music put before me. To me, this means realizing that I'm expected to be versed in as much musical/drumming history that I can hold within me, coupled with as much facility as I can muster, so that I can use that knowledge and skill to create the best drumming performance to any given piece of music that I can come up with.
And I do that, most often, with a set of tools that allows me to cover the lion's share of the things I most often come up with. This approach surely came from starting out (and continuing for decades) as a freelancer. Years of playing all manners of gigs - big bands, cocktail parties, rock session, film scores, country demos, free jazz performances - nearly always many different types in the same week, often in the same day. Through these years and with that schedule, it was not at all practical to have this drum set, and this drum set for that. First for years, I didn't have the money for that. And second, where would I get the time?
No, there was a set of drums in the car - and it didn't 95% of the work I did for decades. Not a set that reconfigured for each setting or style - but one I could pull out of the car, set up, play, load back up - and onto the next gig.
With basically the idea being - I was ready to go without having to go back to the car or reconfiguring. Though, of course, the Dixieland gig on the harbor cruise boat - where you need to be able to literally walk on with your instrument - was either snare only or snare and hi hat. Of course, I could that. But just as importantly - in any other setting, where I had the whole kit set up and only snare and hi hat were required for a piece of music - I could just play snare and hi hat. Same with toms - if had 3 or 4 - and only needed to hear the sound of two.... then that's what I would play. Two toms.... heck they were even set up in the position they would be in a 4 piece - all of those same fills and pattern work exactly the same.
The only set-up compromise on my five piece compared to a four piece is the ride cymbal position. I abhor putting the ride over to the right. And much prefer, keep the right in the same 1-2 o'clock position - but raise it up a bit, move it back a bit and of course, angle it towards me (so that my wrist position stays basically the same having it low and flat. Actually I prefer this set-up so such - that I pretty much maintain it when setting up a 4 piece for myself. (As I've seen many other jazz players do).
So basically a set-up, where BD, SD, HH, Ride and LH crash stay the same - whether I'm using 2 toms or 6. Two cymbals or 10. Because I find I can most be creative, when I'm not confronting re-inventing the wheel regarding my home base.
So no. I wasn't looking at it wrong.... not for me. And as I wrote, different folks have different home bases - or even relate to the importance of a home base differently. There's no right or wrong here - only what works for each. And similarly, that means there are no axioms that define this sort of approach or that sort of set-up is more creative overall. Creative in dealing with compromise yes. But so much of the time, compromise isn't the order of the day - fulfilling the expectations of clients or the other musicians we are playing with is.
my 2 cents...