Naw, in the normal road position one is perched, not sitting, on one's bony structure. If you're fairly upright, you're perched on your ischial tuberosities. If your back is at about 45° or so, you're perched on your inferior pubic ramus. There really isn't much fat to sit on. Your bones push it out of the way. The issue is that when one is perched on one's saddle there's not much blood flow in those squished tissues and they don't like it. That said, it is possible to condition your butt to tolerate that low oxygen environment. One has to do many short rides, like 30' every day for a couple weeks. That usually does it. Some fairly serious riders here don't ride in the winter rain, so they have to recondition every spring, ouch.

This is also the matter of saddle matching one's butt configuration. I've gone through a couple of carboard boxes full of saddles over the decades. Even with a conditioned butt, one won't know if a saddle is just the right thing until after the third hour. One can only experiment, everyone's different. Saddles with only a little padding work best.

You better hope there isn't muscle between your bones and saddle. It would get destroyed by the pressure and movement. A little fat is just right. While sitting down, put your fingertips under your butt and feel your bone structure. See what I mean? It's supposed to be that way. Although if one were so fat one couldn't feel that bone structure, yeah, that would create a problem. Most folks who ride long distances are fairly slim. Most, not all.