Derailed 2’s whole schtick is it makes extensive use of func_train.
Unfortunately, Valve didn’t account for extensive use of func_train when they pushed L4D2 out the door after a year of development, so… much of it ends up being a wonky and buggy mess.
Kudos for the experimentation, however. It certainly wasn’t “just another campaign”… but it’s left in the air whether or not it should’ve remained as just another campaign.