Assists are unusual on DTV; when you fight against a bot you kill it. It doesn't seem necessary in my opinion. The most useful player is the one who kills the most bots and ideally never dies. So the rank order on the scoreboard makes sense the way it is.
I'd rather add an additional column that shows the number of teamkills. It's easy to grief on DTV... Kill 1 teammate and 1 bot, and the scoreboard does not remember the teamkill.