Hello, currently the l4d2_sbt_high_difficulties_finish_off_incapac itated cvar can't be turn off, however it works like it should on lower difficulties but it can't be disabled for higher difficulties. (edit: turning off the target vomited survivor cvar makes the finishing off survivors cvar actually turn off)
also the tank seems to have a difficult time deciding between finishing off survivors and going for whoever is hitting his back.