The tanks described in the OP (wut's flash?) are what I classify as below-average. Average being 1-2 Flash/Overpowers at the start and then just tunnel visioning like they're a dps.

One of the differences between an above average tank and a good tank (in my made up, arbitrary rating system) is that the good tank knows that he's marking not just for kill order, but so that he can build threat on the next target while the previous one is alive (and marks will mostly ensure that dps hit that one next).

A great tank is basically a good tank with better execution. An exceptional tank makes the other players in his party look better than they are.