OCD, I think you have hit the button there. Like many folk here I seem to have and have had an infinity of packs over time. I quite like these various Molle packs as you can add all manner of stuff to the outside, from cameras, to water bottles, to whatever. Many years ago I made myself a clamshell pack, as it seemed a good idea at the time, and perhaps I was ahead of the time.
I tried a 5.11 RUSH pack but really didn't get on with it. There seemed to be so many sections, pockets and pouches, each of which would only weaken the overall pack. It carried poorly and, even with things cinched down, seemed to stick out beyond the average day pack. I remain rather sceptical about the strength and 'weatherproofness' of the zip, too: if that fails, you have little chance of keeping things dry (obviously an impossible ideal in any pack...) but you also stand to lose things when busy, out and about. I have got rid of it and returned to a standard, top-loading sack, organising my bits and pieces into a series of dry bags. If the clips fail on my pack, there is still the possibility of keeping things both dry and together with the drawcord around the top.
As with everything - and I mean 'everything' - it's a personal choice/'horses for courses' but I am not convinced about the merits of a clam-shell type of pack.