The real issue with vendetta verses doom fist
The issue was that the fight was way too easy for both sides.
These are two physically POWERFUL people—both swinging heavy-ass weapons with one hand, using just one hand to wield them. Not to mention, these weapons are supposed to be extremely powerful and dangerous, held by the two most dangerous people in their respective organizations: Vendetta from the Coliseum and Doom from Talon.
This fight should have been spear versus shield. Their fight should've leveled the entire building. **BUT NO—WE GOT A FIGHT THAT MADE BOTH CHARACTERS LOOK SILLY AND WEAK!?!?!**
On Doom's introduction, he's fighting Overwatch's top three operatives at the time (which was basically the only operatives they had): Winston, Genji, and Tracer—none of whom are slouches in combat. He almost beats them all until he pisses Winston off, making him go full rage mode. (And Winston's no slouch either—he clashed with a literal weapon of mass destruction and *won*. Enraged, yeah, but he still won.)
Vendetta? She's simply introduced by killing a mech after her backstory. Compared to Doom's intro, it's not very flashy or memorable, and it didn't give us a proper power scale. Think Shion and Sojourn—their fight gave us a power scale that showed Shion is at least on par with Sojourn in skill and combat ability.
We got to see how good of a fighter Doom really is, but Vendetta is just... eh. So when she was introduced as the new big bad, we thought it was cool—until we saw the terrible fight she had with Doom. It felt like he was about to absolutely molly wop her, and then *bam*—she gets a second wind out of nowhere, tosses Doom out the window, and he falls to his "death."
A VERY stereotypical way to write and end a fight.
Vendetta—with no evidence other than "she trained her whole life"—beat Doom, someone whose experience is as old as Overwatch itself as an organization? Yeah, no. Vendetta wasn't built up properly, and Doom got nerfed because they knew they hadn't built her up right. So they gave her one of the strongest characters in lore to beat (in a stupid, boring fight) instead of actually building her up to *earn* her place among the strongest characters in lore.
All they had to do before the Reign of Talon was give us map lore and more stories about Vendetta. Not drag her up to a level we never saw her properly earn or prove she was worthy of.