To irresponsibly speculate a bit, the feeling I get is that the main priority with Venat as a character was to impart a specific "vibe," or a feeling, about her, that was centered around inspirational player affirmation. (Venat is inspired by You, after all, and in many ways is doing all of this for You. People have noted it feels like there's sort of a fourth-wall-breaking feel to her questions about our journey.) To that end, yes, the walking montage had to be what it had to be - to prioritize "feeling," and also because I think that feeling of affirmation would be impossible to reconcile with a more literal, in-universe version of events.
People have discussed Venat's opposition in that scene being the "faceless Ancient strawman," and yes, that is an interesting choice - because the premise of the sequence would fall apart if we replace the NPC with any actual named and developed Ancient characters. Emet's argument would be coming from an entirely different place - the need to save their people from being trapped in Zodiark. Themis wanted peace between the factions and for everyone to be happy. Themis in particular, I think, is a problem - I'm not sure how you would depict the actual event of her fighting him without ruining the vibe they were going for, given established events. We know that Themis was so distressed by the internal strife among the Ancients that he emerged from Zodiark, leaving it coreless, to try to broker negotiations and peace, and therefore that Hydaelyn must have secured her victory while Zodiark was more vulnerable due to that.
It's a bit facetious and I'm mostly joking, but I honestly get the mental image of Themis stepping out of his cockpit shouting "Wait, stop! Let's talk things through! We shouldn't be fighting!" and Venat replying "PEACE WAS NEVER AN OPTION" and promptly Hydaelyn kicking him in the face.
It's funny - on a personal level, I feel like I've mostly made my peace with Endwalker. My main reservations had to do with the tone/framing around Venat and her conflict with the Ancients - I think she's an interesting and fun character in her own right, if allowed to just be what she is - and that was mollified a bit by Yoshida's concessions in the Q&A about her, though of course I really, really wish it was reflected in the actual text. The rest of the common complaints about Endwalker I generally am not on board with - I absolutely loved Zenos's role in it, I loved Garlemald, I even really like the bait-and-switch with the early Zodiark fight, and I can easily forgive things like pacing issues or the difficulty of writing the Scions as a group when they're not in the focus.
The one thing I find myself still yelling and waving my arms about, though, is JUSTICE FOR THEMIS. That poor kid. I don't really know what I'll do if we do, indeed, end up just kind of leaving him to his fate at the conclusion of Pandaemonium.