Your body can get used to a lot of things, but it takes time, maybe some months. Then after a lot of kilometers, you can be just one with your bike. Also when changing to a more high level bike, can result in some falls. I had around 60000 kms on a ti cyclocross frame with carbon fork, with a relatively hard sqlab saddle, no gel panties, and made a tour of about 5 month, 6000 kms with a 20+ kilo backpack during covid lockdown. Lot of it was offroad terrain. Involved many uphill climbs. No pain occured in my back at all, thanks to the bike and the fact that my body got used to this abuse. On the bike i carried only 5 kilograms. Manuvering, and carrying the bike where it was necessary was easy and enjoyable. But when i try this with even smaller weight on my back nowadays, i really don't understand how i could manage that for a half year. Sure thing i don't want this again...