In my experience, this is only largely true due to the fact that 1. transparencies are positives. You expose and process "in the dark", and thereby largely commit to your final product before you ever see it. Highlights cannot be recovered, the same way shadows cannot be recovered with a neg. With negs, you have the extra, visible and non-committal interpretive step of printing available to you. and 2. 99% of people don't bother to process transparency film any way other than normal.
I do like slides, because i can see what's on the image before scanning or printing it. But that is just one advantage, and I see many disadvantages.
All my work is "hybrid", I use a drum scanner. I minimize digital "enhancement", but must maintain control over contrast and color. I don't care whether I do some dodging and burning on a scan from a slide or a negative, but high contrast of slide films will probably decrease my scope. Adding contrast or saturation is no problem, so I believe that a low-contrast chary-color film is a good choice.
If you apply the theories of speed testing, tonal placement, and development adjustments, you can take care of most of the problems you run into with excessive contrast when using transparency film.
Well, my experience was this:
For a landscape I shot 3 slides, bracketing. One was overexposed, lights were burnt out. One was underexposed, shadows too dense to recover detail. One was in the middle, lights burnt out AND shadows too dense to recover detail. That was my experience with Provia 100F, 4x5", developed in an expensive professional lab. It was not their fault, and the film is among the best you can buy.
Apart from the enormous amount of time I spent for that single shot, it had a price. Three 4x5" sheets, three times 4x5" development, no result. Each shot cost me 2.50 Euros for the film and 2.50 Euros for the lab. So I spent 15 Euros for one photo and had no result. 4x5" and slide film, that's not my cup of tea. With a medium format color negative such a backlight scene is no problem as long as you have a good lens hood.
Many photographers using slide film and digital cameras solve the problem with a color-grad filter, but that creates other problems. How do you control the effect at different apertures? What can you do if the horizont is not straight? It never is, there are always trees, mountains or whatever. I really dislike landscape photos displaying the photographer's ownership of an ND grad filter.
My personal preference is for transparencies. They can be pulled a huge amount compared to color neg. film, so, in my opinion, are much better able to deal with high-contrast scenes, *if* you have the benefit of sheet film or interchangeable magazines so that you can apply the proper development to the right exposures. However, given that most printers wouldn't call for a transparency these days, you would end up scanning anyhow, so again, the difference is negligible. So, what I do is C-41 to save money, if I know I won't need to pull a lot, and E-6 for when I need to pull.
As I do not have my own E-6 lab nor want to pay a fortune for pushing or pulling slide film every time in a high-end pro lab, C-41 seems to be a wise decision. C-41 film processing in a good overnight lab costs 1 Euro here, a 1-hour-photo will charge 2.50 to 4 Euro. E-6 costs between 2.50 and 4 Euros. The local pro lab asks for 10 Euros for E-6 and pulling.
You are already making huge prints, so you should know what works and what doesn't. What are you not getting now that you want to get?
More detail, more sharpness, less grain, enough scope to allow high contrast scenes and some dodging and burning. Natural colors, not Velvia color orgies. The lenses for my Bronica GS-1 are excellent, my Imacon scanner is excellent - and I can not upgrade them so easily. So, the logical step is to look for a film that gives the optimum results for my purposes.
I can almost guarantee you that switching films won't give it to you. A switch in format: yes, but not a switch in film type.
Large format is not for me. I tried it. 6x7 is my personal limit, and I already reached it.