This makes no sense.
The "better" position you're recommending would place your body in a weaker state, more likely leading to injury. Your body's natural state is closer to your first illustration when handling heavier weights.
It makes perfect sense.
You take a weight say 500lbs, you can only handle this weight in your very strongest range of motion, but you get a little bit out of the groove and now you are in a much weaker position, what's going to happen? You will probably get a bad injury.
Now take my method you have no weight on your back and you are trying to move through the hardest possible range of motion, but you can't handle it so either you slip into an easier groove which means less resistance or you lose your balance and have to step back. Either way you're not going to get hurt.
does that make sense now?