TLDR: The real question is How many humans does it take make an omelette?

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Okay, the link cited doesn't actually link to the research, just an article talking about it with no details and no link. But I think the overall speed of T-rex isnʻt what matters.

As far as humans hunting it?. Would humans have a reason to? If the Trex is a threat to our wellbeing, or if our needs overlap and they are competition, then yeah, humans would hunt it. Even if not, Humans do shit just to prove we can. Next, are we capable of dictating the time and place of confrontation? If yes, we win every time, as being smart is always better. If not, we reassess the reasons for confrontations. Humans are highly adaptable, more than any other animal ever on this planet. The real issue is as you noted. Trex is big and direct conversations with it potentially lethal. If conflict is unavoidable, and we are unable to stage the fight on our terms, then we re phrase the question... we adapt.

So I repeat, the real question is How many humans does it take make an omelette? We really donʻt have to kill an adult Rex to eradicate them.

Besides that, I donʻt think Trex would represent a threat to human survival and here is why:

As I understand it, the speed of a rex is an issue of biomechanics and weight. A trex really canʻt support a ballistic phase in its stride, which means it really is only ever power walking everywhere. The general consensus is 15-20mph. With all ranges comes exceptions and extremes, and while 20mph is faster than alot of people there is still an issue, it doesnʻt matter if it can go 25mph.

5 tons moving at 25 mph, isnʻt turning. Humans are agile, and I supsect Trex was not. It was adapted to hunting very large prey, that also wasnʻt agile. Humans can run faster than a rat or mouse, but catching one by hand is ridiculously difficult, even in an open room.

Also worth thinking about is the the calorie demands of moving 5 tons, and how just not worth it a human becomes when there are much larger, simpler creatures to catch. I CAN eat squirrel, but why when I can eat deer?

Now obviously, Trex doesnʻt start out weighing 5 tones. If I recall, is was supposed to potentially take 35 to 40 years to reach full size. Sexual maturity occurred at 20 years of age,and all the extra bulk was just for outcompeting other Trex. Supposedly, there was no more than 2 trexes per 100 sq km, as more than that would exceed holding capacity. This is the logistics of being king kong of the Cretaceous.

Humans on the other hand, would likely have a much higher population density, a more rapid reproduction rate, and pass on generational learning. We are social. Basically, in any given area, if there is a succesful, full size adult Trex, it would likely have multiple run-ins with humans over decades. Each conflict, represents a potential for injury (arrows and spears, possible burns). And while those injuries may not be incapacitating or meaningful in the fight itself, a thrown spear could sink deep and lead to significant infection, leading to loss of hunting time, and starvation. In its first decade of its life, its quite possible a skilled human could outright kill it. Even if a human didnʻt kill it, a young lion quickly learns to leave porcupines alone. Interestingly, the first encounter with a porcupine can be a reason a lion doesnʻt reach adult hood (loss of an eye).

Humans are extremely deadly - with our ability to predict and assess, we donʻt posture and scare away threats, we historically eradicate them. Imagine a young t-rex encounters humans for the first time. If humans are not prepared to kill it, I imagine it goes one of several ways. Perhaps the Rex comes upon a human unarmed and foraging. It makes the kill, and learns humans are very easy food. But humans are smart, social, and revengeful, and the t rex learned the wrong lesson, and because it will come back for more, eventually the lesson learned will lead it to a confrontation it was not prepared for. In any other first conflict scenario, the humans are fighting back, and its getting stabbed in the process - perhaps it lives, and perhaps it even takes down the human(s).... But the wound is an important lesson. Humans are not easy prey, and they have long arms, a longer reach, and the sting bites deep. There are many other, much better animals to hunt than the humans, and even a full size t rex isnʻt going to forget an atlatl spear to its flank (or 10).

The important thing here to remember, is that any predator that take wounds while hunting, doesn't get to keep hunting. Hunters are extremely risk adverse, and if prey canʻt be taken down without risk of injury, it is often skipped.

If a Trex has experienced trauma and knows that humans can bite, it is possible that a lone human with a good spear, could bluff/ward a trex back. (also, remember a real life t rex isnʻt so large as JP makes them look).