[Bungleau]

Personally, I wouldn't worry too much about it.

In my games, 'most everyone gets to be a samurai (as well as a ninja). The end game usually has a zenmaster, valkyrie, assassin, and the remaining three are either samurai or ninja. And most other classes have been covered for at least ten or so levels.

I would move warriors to barbarian immediately (if not sooner). The benefit to hit points starts right away, and you can get the traps and locks skill, too. There's no benefit to staying as a warrior.

Wizards I would leave until they've got their top-level spells; at that point, you can move them wherever. I like barbarian for hitpoints, ranger for vine and fletchery, and paladin for spirit. Then warlock for a while, and finally either ninja or samurai to end the game.