The Novelization actually makes it better. The observing ghost of Barry Allen realizes that Kal-L isn't strong enough, the final punch will fail, and the Anti-Monitor will win. So he travels to limbo, where the souls of all the Anti-Monitor's victims—both those killed normally as well as those who were erased from reality (so at least Ret Gone doesn't mean you completely cease to exist)—are waiting for admittance to the afterlife. Barry runs through them all, borrowing a little bit of energy from each of them, all the billions and billions. And then he returns to the fight, merging with Kal-L and letting him draw upon all that energy, so his last punch has a lot more power to it and is able to do the job. So the Anti-Monitor wasn't just killed by Superman, but by all his victims too. Overlaps with Heartwarming Moment.
It's really hoo-hum by today's standards but all the villains and all the heroes battling each other all over the last three Earths is spectacular. Not just the plan of having all the villains teaming up and outnumbering the heroes 5 to 1 but the heroes band together and with teamwork make it a really close fight.
Negative Woman killing Chemo after he turned the entire sea of an Earth into a cemetary and during the finale she bound and burned the Anti-Monitor for several critical moments.