most of the guys i've played with have been pretty chill and got their own way of getting around that kinda stuff without scream fests on what hits what, what wounds what and what dies.
Unfortunately, not everyone is going to be like that. General rule of thumb is to expect those people to be at tournies, and that you will go up against highly competitive lists. Now whether those people know what they are doing (assaulting after deep striking) is another matter entirely.
I am surprised that your tourny allowed someone to field a forgeworld unit with experimental rules and not have to explain it to you first. (Also what Tau weapon is a large blast, and is ap3?)