I agree with your post. Pain tolerance is different in everyone. The inability to stand up due to structural problems affects us all.
Many aikidoka think that a combination of the two is the answer. Of course, it is an option.
I do not like to "cause pain" though. I think when we create the pain it is a direct link to our center and where our power is coming from. If we lock a joint (kime) and have the uke's structure so off-balance that the only way they can regain their posture is to cause their own pain into the locked joint or take the ukemi it is very difficult to counter or get away. Of course we should lock the uke into a control after the initial technique so they must "give up" in order to get out of the situation.