It's not the same ..
People are saying it will be abused when people want an item and will change class to ninja the item, but you can't do that as you would be required to ask your party if its ok to change class.
There is no problem here.
Except we are talking about DF here, premade parties work differently.
I guess the best solution to this would be, if a player leaves the party allow players to change class before requesting a new player.
Again !!
People aren't reading the whole thread, for someone to change class they would need to ask the permission of the party first so it would not create this situation.