It's not really that out of the blue.To me it felt like Ellie's entire mission in California was futile and wrong, hence the whole massive sequence dedicated to her making an ultimately irrational and wrong decision to abandon a comically idyllic family life in pursuit of retributive violence. Same thing with the pretty on the nose direct parallel between Abby and Lev and Joel and Ellie (lest we forget that Joel was also an amoral murderer of innocents prior to TLOU1)
After a hyper-violent sequence where Ellie literally has to beg for a fight from two dying people, realising she's lost basically all legitimate human value to her life for something that she can't even know Joel would want (Vs wanting Ellie to live a good life), she gives up in a sequence where she is pained and conflicted. Then the ending sequence leaves you on a bitter reminder of what that indulgence of violence ultimately cost.
That is unless you watched scenes on YouTube and kinda wanna be angry. In which case yeah it's total bullshit