Interesting thoughts. I think there’s a difference between a pull that lands out the back and one that rolls out, which is that the offence could in theory have no chance to stop one that is flying over them. A disc that rolls out of bounds has always either been stoppable by the offence, in bounds, or is short enough that in one sense it has received its own ‘punishment’.
I wouldn’t say that landing out and rolling out are necessarily the same thing, both for the reasons I mentioned before (‘good’ pulls sliding out, or rolling out on a severe crosswind even when you tried to keep them in) and because rollers are either stoppable or short.
But I do take your overall point. There’s no obvious inviolable principle such that the rules wouldn’t make sense without it. There’s in a sense no hugely logical reason to choose between ‘pulls must land in the field’ and ‘pulls must stay in the field’. I’d be surprised if the suggested change turned out to be popular though.