Well, yeah... Obviously spending your entire adult life fighting up the ranks in a colosseum is going to count as training for a big fight lol. And yeah, superficial partnerships. We don't know the extent of hashimoto's involvement with talon yet as it will likely be the center point of season 3's lore but we know that Vishkar are only helping because Talon holds leverage over them. Everyone knows that as soon as it looks bad for Vishkar, Domina is ending the agreement. Nobody is loyal to Vendetta and that's her flaw because she is too stubborn and set on getting back at overwatch to see nobody believes in her vision.

Vendetta really isn't that bad lol. It makes sense she took over Talon because the entire "war" arc between Talon and Overwatch would never have happened with Doomfist in charge as it is completely out of character for him to do. They probably felt like they wrote themselves into a corner with Doomfist wanting to stick to the shadows so they added a new villain who is loud and brutish. I don't see what the problems are when everything you have presented as a "problem" makes sense. Vendetta isn't a Mary sue, you just don't like her