Alright, my belief that staves were useful weapons hinges on the following.
1. They only work in one on one fights or small group battles.
2. They only work against unarmored fighters
3. You need some room to work.
4. They're a peasant weapon. Most of the world, most of the time, had some kind of sumptuary law forbidding peasants from owning or carrying swords, spears, and various weapons of war. Sticks are more or less free.
5. My idea of a stave isn't a stripped sapling so much as a 6-7 foot piece of hardwood heart wood with a good, straight grain. I have a purpleheart staff that is 6'6" long and weighs about as much as my longsword. It's a somewhat different animal than a rattan stave, and I'm fairly confident that it hits at least as hard as a Louisville Slugger.
So, you advantages in that kind of fight are the ability to reach out and touch someone eight or ten feet away with a lot of force, block in many directions, attack in many directions, and use the long piece of hardwood as a lever to hit people with considerable force. It's very obviously of no use in a war, but when the conditions are right it can be effective. Admittedly, all apocryphal, but it's what I've got without hitting up the library.
I suppose it's worth taking into account that different weapons work for different fights. A rapier isn't much use against full articulated plate, spears are difficult to use in personal combat against sword and board, archers make mockery of two handed swords, one pike man is worse than useless, firearms were substantially less effective than bows until the reload time and accuracy were dramatically improved, Crossbows are more dangerous against plate armor because of the specific characteristics of the projectile, but they don't have the range of bows and they're much, much more expensive. Fighting with two swords was, the best of my knowledge, almost never done, but it's quite effective in sport fighting.