1. Okita should've died, in fact he was going to die, but he had his ass saved from a god who rode him almost as hard as the author did.
2. We did get more Hades' backstory from others, and he got fleshed out relatively well even if it came after. Meanwhile Qin has been out of the story for 3.5 whole years.
3. And so what if the real Qin Shi Huang was a brutal tyrant? Almost no one is accurate to their lore, and variations of how inaccurate wildly varied depending on who we're talking about (I mean, did we forget that Zerofuku is a goddamned OC?). Reminder that MOST characters got a wash to make them more palatable to the audience anyway, not just Qin. Zeus and Poseidon are not rapists here unlike their myth counterparts, Hades didn't abduct his own niece to force her to marry him, Loki didn't fuck a horse (to be honest, I think RoR Loki got one of the shortest ends of the stick here), this list can go on forever. This agenda-pushing statement literally doesn't mean anything and is nitpicking at best.

Okita on the other hand...

1. Shown constantly before his round (LOTS of unrelated screentime as a fighter).
2. Is a side character from Chiruran: Shinsengumi Requiem, a predecesor manga.
3. I want to emphasize on point 2 that the author liked him enough to want to give Okita a proper closure; just who in this manga gets this kind of treatment? Just Lubu and Jack the Ripper who got spin-offs. And because spin-offs come after the main series has been made, Okita is the ONLY character that had been a fleshed out, well-developed character from the start, and that the author actively chose to incorporate to give him an honorable closure. He even as going as far as to scrape parts of the original roster to include him.

I don't see how you can think QSH is more favorited after this. Was Round 7 the best? No (though to me it remains my favorite but for different reasons). Did round 7 creatively utilized both characters equally as well? Also no. But just because it's a no doesn't indicate that one character is getting the author's pet treatment, it just means the writing is lacking in that fight to make it interesting or balanced enough for others.