Is Skeletonwitch really big enough to do an 85-date North American headlining tour?

Yeah of course. Something's gotta give eventually. The trick is prevailing through that though. During those early years as a band, you kind of have to take it on the chin and deal with it. Lots of bands use the phrase "eating shit" when starting out, and by that they don't just mean eating bad food, they mean it with regards to every aspect of the road. It's a terrible terrible life and you have to be really dedicated to being a musician to do it. It's not a vacation, and day offs on tours (especially small headliner tours or DIY tours) can absolutely cause more damage than not.

And it gets even worse at the "pro" level. If you're supporting a big band, and that tour has days off, sometimes it can't be helped. You're at the mercy of the agent who booked that tour. For the headliner of that tour, making 5, 10 or 15+ grand a night, a few days don't do a whole lot of damage, and help to make the show better. Just like what Stingray said. But for the smaller band that makes 2-500 a night forget it. It's a guaranteed loss of money. Some bands are prepared for that loss, and if they're sharing a bus or van with the headliner, they obviously can't book "off dates," so they have to just deal with losing a substantial amount of money.