I guess you could say that bigger formats are always a bigger hassle.
Before the digitale era people also used to switch back and forth between bigger and smaller formats. 35mm film is easy to use, you can pack a lot of photos on one film and it's light weight, doesn't need as much power, less vibration etc - and in many cases it's more reliable. I remember that my Hasselblad sometimes used to jam during shoots as well but my AE/A1 never had any problems what so ever.
I guess the question is how much trouble you 'want' to go through to achieve the quality you desire. If you don't want or need the MF 'look'/'feel' then it'd be a bad idea to use one. If you want the LF 'look'/'feel' then even a medium format camera won't do.
Having said that I'm personally very satisfied with my PhaseOne experience on the 645DF+. The only times it 'gltiched' were caused by me and my inexperience with the camera or bad handling of the tethering and 1-2 software issues. Yes, CaptureOne crashed on two occasions during shoots for magazines - but one click and it worked again for the rest of the day. I can live with that and nobody complained or was annoyed - they were just happy to see big, detailed files appear instantly on the screen instead of having to wait for the photographer to switch memory cards.
I will definitely get a second body soon - just in case.
But the last months have been very enjoyable, much better than my experiences with Canon and all the other brands I got a chance to work with and use over the years (except maybe for the Hasselblad 503CW). However - if the problems are mainly due to leafshutter jams I can't really comment, I only have the 80mm LS lens and always rent the other LS lenses (35€ for a day is reaaally reasonable!) and they never gave me any problems.
I guess it could be another story if I used them daily.
However there are a few things about his story I just didn't understand:
- Why didn't he just get a used 645DF(+) body as a backup? Does it have to be a new one if it's "just" a backup? Even a refurbished camera will be much cheaper
- Why double up on the lenses? If you need a backup a 75-150 will do fine for most applications and it covers a huge range. Combine that with a wide angle and that's it - most likely you won't even need the LS version, he's obviously not relying on the fast sync speed if he's content with a Nikon/Sony gear. Again: get used versions and they're just as good for much less money.
- Second back? Get a used P65+. It's a backup after all and has the same sensor as the 160, is just as fast....
To me a "backup" means something I can use in case my primary equipment fails. It has to be good enough to finish the job, not equal to or better than my primary equipment. If you want to buy everything brand new you can't really complain about the price, especially when there are a lot of options that are just as good and useful on the second hand market.
But: If his style does not need MF and he himself is content without it, then the whole price and reliability debate is a moot point. A magazine doesn't care if the photos are shot on a small, medium or large format camera, whats important is that it's good enough to print and that the content is good.