Point taken - but for northbound change at Camden Town this doesn't apply in the same way. And anyway, given the major congestion which is common just with people leaving and joining the tube at CT, it wouldn't need anything like 50% of travellers routinely needing to change there to make the situation impossible. So a complete split of the line isn't an option anyway until there's lots of money to rebuild CT station. Also, don't forget that if a complete split included full separation at the southern end too, that might not be ideal if there are different service needs on the two (one-and-a-bit?) southern branches.
Anyway, I personally think passenger convenience is best served with the current situation - heading north from the centre of town, you can wait (if needed) for a through journey, or you can opt to join the interchange scrum at CT if you want the possibility of saving a minute or two; and vice versa heading into town from the northern branches. Of course I do understand that some people prefer the "neatness" of all services being a simple point-to-point pattern, and I know that such a system can give a higher theoretical maximum frequency. But it's less interesting.....