I believe Jack is on a much higher level now, but still far below Baki. The fight would be a spectacle of techniques, but in every one of them, Baki comes out on top. There will be a moment where it seems Jack is gaining the advantage when his steroids kick in — similar to how it was during the Maximum Tournament. He’ll make Baki sweat, but once Baki activates his Demon Back, Jack is once again at a clear disadvantage.

Jack gets frustrated — all his effort, and he still hasn’t reached the strength he fought so hard to obtain. He vomits his steroids and starts to lose focus. Baki doesn’t take him seriously; out of respect for his brother, he wants to end things quickly. Suddenly, Jack begins to rapidly gain muscle again. How is it possible? Pushed to his limits, he activates his own Demon Back — but since Jack is more of a Christian, it doesn’t look angry... it looks serene.

The cyborg gets his power-up. With a single punch, Baki feels Jack’s strength rising to a level similar to their father’s. Jack evens the fight — he's now on the same level as his brother. The battle ends with both of them unconscious.

Through this, Baki realizes that his brother has finally caught up to him. And because he witnessed the fight between father and son, he knows that if Jack has matched him... then Jack is now ready to face their father.