Reasons each fighter was picked
Lü Bu: One of the few fighters that can actually match Thor, at least with base Mjölnir, in raw power. Would've stomped Thor if Brünhilde's prediction about Járngreipr had been right.
Adam: Picked due to Brünhilde not wanting the gods to get the lead, put against Shiva. Adam would've been a great match against Shiva since he's one of the best hand-to-hand fighters and he outclasses Shiva is raw power. Divine Reflection is the perfect counter against Tandava since it'll just copy it no matter what.
Sasaki Kojirō: Elected himself to go up, nonetheless, Brünhilde gets the final say. Kojirō is basically the only fighter that can keep up with Poseidon's speed, especially after training nonstop for four hundred years.
Jack the Ripper: Picked specifically because Brünhilde knew Heracles would be fighting due to his honor and how greatly he's respected. Due to his honor, Brünhilde fed him to Jack who fought entirely with tricks. By the time Heracles made the first step, Jack was on step fifteen. Heracles is also one of the few gods that would let Jack get away with most of his bullshit.
Tameemon Raiden: Put up against Shiva since he's only of the few humans that can match him in raw power and keep up with him in a fist fight. A class between martial artists, Raiden may be a little slower but he's able to take multiple hits well, which is good since Shiva has Tandava.
Buddha: Buddha was picked by Zeus to fight and betrayed the gods, Brünhilde had counted on him switching back to humanity but had no influence over who he'd fight and just hoped he'd merc'd his opponent.
Qin Shi Huang: While outclassed in terms of power, Qin's fighting style counters Hades's use of brute force. Bubbles basically ****** Hades over since he had no way of avoiding them by the end (Coating himself in blood was a good idea, but it was done to activate Demos which led to his defeat)
Nikola Tesla: Tesla sure....He sure.....Um, he was sure able to land one direct hit during his fight, yeah. I guess that's better than none. Was able to barely survive Chaos by using Tesla Coils, not sure if Brünhilde even knew about this technique.
King Leonidas: Much, much stronger than his opponent and can take a hit really well. One of the strongest humans, Brünhilde was probably hoping that Apollo's cockiness would lead to him making a dumb decision that would end with Leonidas scoring a direct hit on him (More needs to be seen with this fight)