Humans have always killed predators. A "spear band" as you put it is essentially what an old-fashioned whaling crew is, and they killed the largest predators in history - sperm whales. A pack of primitive hunters could take down a T-Rex, or anything you can think of. It just takes ingenuity.
@FollowingHim, you are disregarding most important fact.
It's not 1 predator vs human group where you can easily play smarter tactics. You can face one bigger predator by surronding him, using fire and spears where he is one feeling death anxiety.
It's group vs group fights. And predator groups means intelligence. In worst case it's night attack by T-rexs in forest who's approach can't be seen or heard till they are in your face. Verdict: Total wipeout of human group.
And even if approach is detected on time, then human ground is surronded and hope that some spears pointed outside with some fire will be enough.
And don't forget vulnerability of pregnant women and small children. Group can't run, it must fight.
And so far nothing mentions differences in size. Even sabertooth or bear would be real problem for group, nevermind something pack of something 10X more dangerous.
And since predators have superiority in senses they choose time and place of fight. Not humans. In military terms, predators are ones having iniciative which means fight is on their terms.
Survival means that species can easily accept worst-case scenarios which don't happen often. Triceraptor herd in worst case loses one member (not whole group as humans) and usually can fight out attack. So Triceraptors are fine.
Think a little. Reasonable security means moving and living inside roman style fortified camp. How to they get food? Problematic to grow enough food inside camp and getting outside is dangerous. And moving out means building new camp for every night. A lot of time spend and energy spend keeping dangerous animals out, instead of providing food.
And so far nobody has mentioned needed minimun size of human group for survival? 50,60 or hundreds. What I know is that larger group is, they will more depend on agriculture or be forced to follow big herbivore group. And big predators would like to do some competition elimination. And how can you follow herbivores when you must spend at least 4 hours of camp work (both building news and taking stuff from old)?
And what about sea? By sea, I mean megalodon babies of great white shark size swimming in coastal waters (1 km from coast) because their natural habitat open ocean is too dangerous. Would you now go fishing in primitive boat wiyh some nets.
Just because we had won in current history with current start conditions as were when humans had arrived, doesn't mean we would won if starting conditions were different.