I can't address how CATIA handles assemblies, it sounds a bit to me like components aren't really definitively constrained? I recall another CAD system that I learned prior to Creo that didn't either, so there could be a discussion on CAD theory here but none of us are probably qualified to debate it here.
I do know positively, that your statement about Creo only being able to assemble one part at a time is blatantly false, but I can see where the basic user might believe that to be true. If you hate Creo so much, and you're such an expert on Catia, perhaps you should stick with Catia. I would have a difficult time and struggle doing everything I've done with Pro-E, on Catia.
I have been impressed with some of Catia's surfacing, and I did complete some Catia solid modeling tutorials, and I am of the belief that Catia, as well as NX, appear to cater more toward the user's needs, where PTC seems to focus more on sales and marketing.