IMHO, the old adage "Horses For Courses" is still highly valid … IF … you are able to define the different "Courses" you will be running.
Personally, it is a crystal clear distinction for me. I can line list exactly how I use each piece of gear and why. When and if technology alters that, or my work demands change, then that list can change.
How other's may use certain gear often has zero influence on my choices … unless they are engaged in similar tasks:
For example, use of 18 to 24 meg 135mm cameras for weddings I once did on a regular basis. There I needed AF speed, higher ISO, good zoom ranges and choice of primes with faster apertures, a good speed-light system and dual card capture. That usually meant a Canon or Nikon. I just sold the last of those types of camera (a Sony A99). At the time, the Sony Mirrorless cameras couldn't quite make it for weddings in the same way. They just now are getting closer, but I no longer need a wedding specific system … so I now have a Sony A7R and A7R-II.
MFD is much easier for me to distinguish from any 135 format system.
Every MFD system I've had uses leaf shutter lenses. V system sync to 1/500. H system to 1/800. Now a S system to 1/1000.
It isn't a matter of just using leaf shutter sync when needed (which does frequently happen) …
I also create visual scenarios that require it. It is part of my conceptual visual thinking.
The Sony A7R-II can NOT do that. On the other hand, like the Sony, the S camera can shoot focal plane shutter work with the same set of leaf-shutter CS lenses, and the S lenses are fast aperture for MF.
For example, one of my shooting partners and I will be doing a beach shoot in Florida. We will get ideal early light and segue to not so great midday sun. Using a Hensel Porty 1200L pack we can over-power that sun … but the best his A7R-II can do is 1/180 sync … I'll have up to 1/1000 to control the background ambience.
Because I use lighting a lot, that advantage alone makes MFD worth it to me … and it isn't the only reason. However, those other reasons have been beaten to death in another similar thread.
Size is not an issue when in studio … the camera is on a heavy duty tripod … on location I have transport options including a beach trolly with fat wheels, When driving I ALWAYS take the MFD kit as well as a smaller walk-round no-brainer; on planes I use the Airport Extreme roller case.
I do appreciate the ease and convenience of the Sony mirror-less cameras … which is why I have that "Horse" to run certain courses.
- Marc