Torakage are one of my favorite models to play, with any master. They always do well, whether its running schemes or just causing my opponent to spend more AP then they would want to remove them from the board. Oiran are not as effective though, but their +1 to WP is nice at times. I still don't understand why everyone says these models are worthless.
As for the original post, i don't think the models listed are worthless because of wave 3/4. Izamu isn't useless because of Yasunori. They both fill a similar role, but if i weren't taking any other Oni, Izamu might be a better choice then Yasunori. There is no model in this game i have played that feels like i was at a disadvantage if i took it over a different model. It really comes down to just playing what models you like the look of and play style (not to mention wave 4 models are the newest, and it feels like the newer models always gets move love from the player base then the older models in these types of games, even if the models are just as good.)