Bone to bone in the seated position is much more stable if you do it right.Well over 95% of all deer I have ever shot were shot with my elbow resting on my thigh, or the outside of my forearm resting on my knee. I never shoot with the elbow bone resting on the knee cap. Bone on bone isn't solid. I have made 10 yard shots and 200 yard shots using this technique. I hunt sitting on the ground more often than not, and if I'm walking and there is no tree to brace against, I take a knee and use this technique.
I have shot several deer free handed, up to 80-100 yards. I don't recommend it for everyone but some guys can shoot fairly well free handed.
I can honestly say that of all the deer I've taken (no idea how many, but well over 100) less than 1% were shot using a rest or a rail.