You're correct that the diameter matters too, and it certainly shouldn't be ignored. The negative offset the OP is running is also a factor (maybe even more so than the width). Many things go into fitting wheels/tires on a truck so we obviously can't say any one thing exclusively will make or break a good fit.
That said, based on the experience of various tires on these particular trucks, it seems the diameter can work without rubbing. I'm running 285/75/18 tires as are others on the forum, and I have no issues with rubbing. Those are 34.8" diameter, so if someone is having rubbing issues with a 35" diameter tire wider, it would suggest the width is the culprit.
Again, that's ignoring the offset of the wheel which may not be helping.
As for the tire width based on dimensional values alone. While your synopsis of the widths are reasonable and a good place to start, there are a few things to consider. Much like diameter, the sizes vary a bit by manufacturer. The dimensional sizes are a good general guide, but they are also effected by the width of the rim the tire is mounted on. So for example, if a 285 tire is 11" wide when mounted on an 8" wide rim, it will measure 11.4" wide when mounted on a 9" wide rim. The rule of thumb is 0.2" width change on the tire for every 1/2" change on the wheel. The thing occurs when going narrowing, just the opposite direction of course.
All that to say that 285 may not necessarily be 11" width and a 315 may not necessarily be a 12.5" width. Factoring diameter, width and offset all play into what fits and what hits. That's why there are so many threads on nearly every automotive forum. Because there isn't a magic number that fits every application, since other variable play into it too.