"Huge nebulae or star fields are quite awful in the small fov of Cassegrain-based scopes."
The C5 delivers a 1.3 degree TFOV with a garden variety 32mm Plossl. Which huge nebulae or starfields are you observing that do not fit in a 1.3 degree FOV?
If you wanted to get crazy and mount up a 2" SCT diagonal on the C5, your TFOV can be over 2 degrees - Pleiades swallowing, but that would entail a heavy 2" wide field eyepiece, too. Sticking with 1.25" eyepieces, the C5 is actually quite versatile in TFOV terms. The 5" of light grasp, too, will pull in much dimmer nebulosity whisps (and also work better with light sucking narrow band filters) than a little refractor.
I've done both; backpacked in 60mm and 72mm refractors and 90mm MCTs and the C5. There's almost nothing any of the three smaller scopes would do that the C5 didn't do a whole lot better. The real issue is the extra diameter of the OTA and what else from the backpack it displaces. Mountwise, I'd not use a refractor on anything lighter than a Dwarfstar, and the Dwarfstar works fine with a C5. The DSV-1 is way to big for backpacking IMO. Photo heads are way too feeble for astronomy with any of these scopes, IMO. The C5 is as light and as short as a 70mm fast refractor. It displaces approximately 2x the volume, though. If you're carrying a Gregory Denali pack (100L), the difference between a C5 or 70mm refractor is pretty trivial. On the other hand, if you're carrying a small 35L-45L light pack, the C5 would be prohibitive (as I suspect would a 70mm refractor), and binoculars would be your chum.
Small fast refractors are a lot bigger and heavier than most folks think. The C5 is a lot smaller and lighter than most folks think. I had to actually play with all of them to realize that. The scopes I've experimented with thus far are the C90, C5, AT72ED and AT60EDT. If I am doing a single night session, using a backpack, I actually skip the backpacking backpack and instead use a big photography backpack. I can fit the OTA, mount head, a small stove, 1P tent or bivy and other accessories in the main compartment, and strap the tripod and a sleeping bag in compression sack on the outside of the pack. I have a Mountainsmith Parallax for this purpose.