I think how you define "fast" may be context sensitive. Seven tons moving at twelve miles an hour is a huge amount of momentum. Being able to move at twelve miles an hour in heavy vegetation could be considered just as exceptional as a cheetah's 40 mph on a flat plain.

My best power-walking speed is four mph. For all that the NatGeo article tried to make T Rex sound slow, I think I'd have a hard time maintaining 12.1 mph for long enough to get away. And I'd have to go around barriers T Rex would just lumber through. I thought citing the extreme case of the fastest human runner at 27mph was deceptive--I'll bet my "sprint" speed is barely 12.

As one scientist in the article noted, though, morphology only takes you so far. T Rex looks to me like a machine for boring holes in jungle, but that's just morphology.