I've been out of town. What you haven't done is, while sitting in a soft chair, reaching down and pushing your fingertips into your butt. I lean forward quite a bit on the bike, so I perch on my pubic ramus. I can easily push my fingertips right into that bone, nothing between my fingertips and the bone, hard as a rock, other than a little skin. Of course a "little skin" means the whole dermis, which feels like it's a few mm thick. I tried contracting my glutes while doing this. Didn't make any difference. I could feel them contracting, but no additional tissue appeared between my fingertips and bone.

Maybe you aren't the same as I. I've been riding for decades on pretty much the same type of saddle and in pretty much the same position, so maybe that has modified my butt tissues. I haven't experimented on anyone else's butt. That said, the whole idea that there would be muscle tissue active between bone and saddle is a bit odd. We've been sitting on hard surfaces for at least a million years. DNA is pretty good at figuring out what works.