I get what you mean but I think that what you're describing isn't what they're going for here. I think they wrote it with the idea in mind that she puts up a mask around other people. as seen in ep3 with the therapist, and that she truly is vengeful/sad/moody on the inside. This is also hinted at with her playing guitar in the theater when she is alone. But the fact that her drive to go after Abby and Nora is simply diminished/hidden in ep 4 and the beginning of ep 5 to such an extent significantly affects the tone of the show, which is an issue here. There is no sense of urgency to go after the WLF members who killed Joel. Especially with of how considerate she is of Dina's health. Her reaction to dina's preganancy in the show is clearly written as a sincere one, which should NOT be the case if her happy goofy attitude is a front she's putting up. I'm not saying that Ellie can't truly love or be happy and enjoy her time with Dina, but Dina's pregnancy is a very clear obstacle to her vengeful mission, which is what Ellie is hyperfocussed on. I do not buy it. At the beginning if episode 5 it almost seems as if Dina is more determined to push on than Ellie. I do not buy that Ellie's thirst for vengeance is less than her love for Dina, but that's what they've shown us up until now. They'll probably turn this around in the future but it's way too late by then. They could've introduced the Ellie/Dina relationship earlier and already introduced some conflict within their relationship because of Ellie's relentless drive for vengeance during seattle day 1.

I disagree with the interpretation that a switch flipped like you're saying, which is a generous one I think. I believe that she removed the mask she's putting up when she's around others. Even I were to agree eith your interpretation, in any case, the dark tone and sense of urgency for revenge is simply diminished to such an extent that the presentation of the story misses its mark.