In the King Kong movie Kong holds his own against 3 T-Rexes and in JW the I-Rex has trouble with just 1.
Kong has opposable thumbs so he can pick up weapons, throw stuff, etc. and he also has a long reach. They also show the T-Rexes biting Kong and somehow it doesn't even puncture him that bad.
I only see I-Rex winning if he is cloaked and can get a surprise attack.