One thing I thought of about leveling, breaking a group apart, so you only have one person at a time, doesn't make much sense to me. Here's why:
Say you get 300XP for one monster when you have one person in a group. Each person would have to kill the same monster once, so that they each get 300XP. That would be three encounters with the monster. Yet, if you have a party of 3, everyone gets 100XP for killing the monster. To get the 300XP, you still have to kill three of the same monster. In otherwords, no matter which way you do it, you still have to kill about the same number of monsters in order to keep everyone at approximately the same level.