As dark a place as that would put Ellie in, she wouldn't become Kratos or Guts. It feels like a pull, like they took her character and just slapped a big sticker over her forehead that reads 'REVENGE', so that the game could be uber dark and therefore more intense and hardcore than the first game. It also just feels like such hackneyed way to explore a dark theme. Especially for a setting that wants to feel grounded and realistic.
And she doesn't even seem to be in THAT good of a mood at the start of the game, she just appears to have a nice stable day-to-day life with friends and some maybe-romance. Nothing about it feels like she's frustrated at lacking agency, and like we're just waiting for something to ignite the fury within her. And nothing about it feels like she's so happy that anyone stripping it away would send her into a blind rage. She still has Dina, a safe home, and the knowledge that she's part of a community to works to help and protect people.
This is why the events of the end of the first game being played off as almost tertiary (and out of order) is such a waste. The flashback where she finds out the truth ends with her just saying 'I'll go back (to Jackson), but we're through'. This really needed a rant from her to make it clear how lost she's been and still is due to what Joel did. (And then actually follow through on that; no Dina, no Jesse, just Ellie lost and alone.) Remember Elena's rant in Uncharted 4 to Drake? That's what we needed for Ellie, but on a scale of having been lied to for 4 years. This could've, and honestly should've, been the catalyst for Ellie's decent into darkness. You wouldn't even need to kill Joel. It would've been so much more interesting to see Joel realize what his choice did to Ellie, and how saving her for his own self interest turned her into a monster.
Not that I'm saying the game should've gone that dark at all, since I think the first game was already plenty dark, and by amplifying that aspect I feel the game truly just overindulges in nastiness. But IF they wanted Ellie to go crazy with rage, it should've been due to finding out what Joel did (and also how he coldly executed Marlene, seriously, why was that never mentioned again?), not due to Joel getting killed. As is it just feels like the most typical revenge motivation that the game can hardly even tell well enough since the narrative is out of order.