I think Luna needed a moment, just one moment, to peel back her dutiful attitude and just act like the kid she was never able to be since that attack on Tennebrae which took her mother. We've seen the letters they send to each other quite frequently, we've seen what's written in them, we've seen Luna fight for Noctis at the trial of Leviathan, and hell I don't even think screen time is her real problem, all of the proper elements of their love story are there except for one which is key in selling it to the audience. We never get to see Luna truly open up, the closest we get is that scene with Ravus but even that seems to be coming from a dutiful angle.
I want a genuine scene between her and Noctis where she just brings down her walls for just a second and lets us as the audience connect so we can see the part of her that Noctis clicks with. If we can see the Luna that Noct sees for even a moment then I think her character will finally make sense and it will also put the rest of her scenes into a new light because then it's not that she can't be quirky and fun it's just that she's never had the chance to be that way other than for one fleeting moment with Noctis for the first time in like 10 or so years.
It's probably a pipe dream but I really want that night out before the trial of Leviathan to be a thing for this reason, have Prompto distract the guards outside Luna's place while Noct sneaks into Luna's room via warp strike, have him warp her out and take her through the city in disguise, and just have them open up for real. To preserve the aspect of them never getting to fully experience love they could have Prompto call Noctis and inform him that the guards are going to check up on Luna in a few minutes just before the two can share a kiss or something and he has to hastily warp her back. Perfect way to weave this into Episode Luna could be to have it as small flashback sequences interspersed throughout the episode as she fights in present day to save Noctis so that we get a sense of why she's fighting so hard to change his destiny.
Oh well, guess we'll see how Square handles this going forward because honestly playing as her and seeing more of her will have meant nothing if we still can't connect to her side of the romance and don't see what Noct sees in her.