"If you fall on your spine..."
Seriously? Do you guys make a habit of falling on your back? When tussling with a bad guy, even if you go down backwards, aren't you moving side to side? Sorry, I just think this is a stupid argument. I'm going to be more worried about the knife the bad guy is trying to shove in my gut if things come to that.
Uncomfortable when sitting? Adjust your lumbar support. Fixed.
Now, as far as the shirt riding up- this is absolutely true. Getting in and out of the car, it's become a habit for me now to reach behind with my left hand and double check my shirt is draped over my gun.
When sitting in church, I have a tendency to lean forward, studiously. (Paying close attention keeps me from napping.) This is another concealment problem- there's not a lot of vertical support in an SOB holster, so the butt of your grip will shoot straight up in the air and make you look like Quasimodo.
Last thought- I have an ambidextrous safety on my 1911. In an SOB holster, while seated or moving around I have knocked the safety off more than once. There's still the grip safety and the trigger is covered, but this is something worth noting.
As long as you practice withdrawing your firearm from the holster, unnecessary sweeping of the muzzle across non-targets can be easily remedied.
I've carried a full size 1911 in an SOB for the past 4 months. For reference, I'm 6'0" and 190 pounds. It works just fine, and may be a good option for you. In full disclosure, I'm waiting on a custom holster that will be strong side on the hip, and I'm hoping to move my gun there full time to avoid the hunchback effect. But the typical reasons people poo-poo SOB holsters are fear-mongering, juts repeating what they heard, or forgetting that not everyone is built the same way.
If you want to try it, go for it. Don't we all have more holsters than guns, anyway?