A shark doesn't immobilize it's prey. I just takes out a chunk, backs offf and waits for it to bleed to death.
Komodo dragons take a bite the follow the prey until it bleeds out, or sucumbs to septic shock. (Komodo dragons have very dirty mouths).
Fossil T. Rex teeth have serations with septic bacteria breeding pockets at their bases...
Why would T-Rex even need to run fast? Their prey was very large and very slow. It seems to me as though the controversy is moot.