So, is there any reason to do a traditional wash with a hose and water besides a vehicle with mud/dirt or other heavy soiling?
I still feel pressure rinsing a car down first with water will always be safer. Regardless if its followed by a 2BM or a rinseless wash. Since most people feel this process is not inline with a rinseless wash, if you eliminate the pressure rinsing, and apply that step to a 2BM exclusively - the 2BM will always be safer for paint.
Anytime you remove dirt without touching the paint before touching the paint - you have less chance of marring the finish. Since a traditional rinseless wash skips this step entirely (you just wipe dirty paint) - I feel it inherently can cause more marring just via the process.
While rinseless washes do a good job - an abrasive dirt particle that is not removed prior to touching the surface is a particle that is drug across the surface and can cause micro-scratches in the removal process during a rinseless wash. Several of these micro-scratches constitute a swirl. It's common sense that any "soap" can only remove particles so large without scratching.
I don't believe rinseless washes have some super technology that is able to completely compensate for this to any significant degree for various grits and sizes of dirt. They may a little - but the cutoff it not clear. Nor is there a universals cutoff to various degrees of soiling and it's abrasiveness that may be on any part of you paint when you do a rinseless wash.
The point I'm trying to make can clearly be seen with a dirty wheel. Most detailers that know their stuff will hose down / pressure wash a dirty wheel before agitating it with wheel cleaner and tools. The reason is is that a large portion of the dirt on the wheel is quickly removed by just pressure washing the wheel.
The difference is, most factory wheel surfaces' paint are not as scratch sensitive as the paint on the body panels. Just spraying cleaner on a dry wheel and wiping it off is not an effective way to clean a moderately dirty wheel. Rinseless washes may work here - but generally not well if the wheel is pretty dirty.
So, my advice is to always hose or pressure rinse the car down first - regardless of what type of wash you do. This will remove a good chunk of the dirt touchlessly - before it has the opportunity to be drug across your paint.