One, this fight should have happened during the day...
Oh, because of the 24-hour deadline. Oops!
and two, if it's a fight to the death, how come no one dies, or at least fake died like Amok Time or Code of honor.
It was your standard "fight to the death" story where the hero has the opponent at his mercy and refuses to kill them. We've seen it a million times, including Kirk and the Gorn in "Arena" (and recently in Guillermo del Toro's
Trollhunters animated series on Netflix). Cisco was just a bit more informal about it. "Around here, we don't roll that way."
The whole "combat to the death challenge" was rather a silly notion for a futuristic transdimensional cop of sorts.
As current events in the US demonstrate, cultures can regress in their values. Earth-19 had suffered a brutal interdimensional invasion and adopted draconian measures to restrict further ID travel, probably for fear of attracting the attention of more invaders. Maybe the trial-by-combat rule is some legacy of their time under the invaders' occupation. Or perhaps, as is often the case in real life, being occupied by an invading culture caused them to re-embrace some older traditions that were distinctly theirs, playing them up as symbols of their cultural identity even though they'd largely fallen by the wayside before the occupation.
She should have been named Vibette as she was nothing like Gypsy.
And Cisco is very little like the original Vibe. Both of the original "Justice League Detroit" characters were blatant ethnic stereotypes -- Gypsy was a stereotyped Roma whose illusion powers were based on the stereotype of "Gypsies" as thieves and frauds (even her name is an ethnic slur), and Vibe was a caricatured Puerto Rican break-dancer with a heavy accent. The show took its own direction with Cisco, so why shouldn't they do so with Gypsy? Not to mention all the other Berlantiverse characters who are quite different from their comics counterparts, like Felicity, Caitlin, Jax, Guardian, etc.
I didn't care for the Iris-Wally team-up, which felt contrived. It was irrational for her to be so reckless so she could write a good article for her newspaper.
Two words: "Lois" and "Lane."
So what? I could see it being creepy when the doppelganger looks exactly like you. That would be like being in a relationship with your clone. But that's not the case here. Even if they are each other's doppelganger, they look nothing like each other. It's just a man and a woman who are attracted to each other.
A biological sister and brother don't look exactly alike, but that doesn't make it okay. Incest taboos have never been about appearance, but about biological relationship. A parallel-world doppelganger could be considered a twin sibling. At the least, a relationship with one's own alternate self could be seen as narcissistic.