Flashbacks are typically disruptive to the narrative flow and takes you out of the events you are interested it. Especially in a game where we're supposedly the ones making the decisions. The reason why they usually feel clunky is because they just are.
Whut? Just no.
Flashbacks can be done wrong or can be done right, even masterfully, as Rashomon or The man whot shot Liberty Valance show us. Just to throw two examples. They're a device, a technique, and can be as good as the author using them is.
In fact, as has been pointed out, Eva has already done one with the polaroids (not exactly a Harry Potter's pensieve, but still...) and it worked, didn't disrupt the narrative (more like pushed it: making Lena close the door for good to reminiscing Axel or opening it more than before), leaving those decisions to the player while explaining more the background of past Lena (before she was in player's control), and didn't feel -at least to me- clunky at all. Maybe we should trust she knows her stuff?
If you want to refer to past events or make them relevant, then you give your character traits and impressions that they will eventually explain by sharing information with another character.
That's just exposition, and while it can also work more often than not breaks the "show, don't tell" golden rule. Especially if abused and not employed in concert with other narrative devices, it grows old pretty quick and can become boring FAST. Was one of the earlier and most noticiable flaws of GoT, for example, they even had to throw sex in (falling into the infamous "sexposition") if only to make interesting two guys "explaining and sharing information" instead of showing the viewers it.
I for one am quite happy with Eva making the calls here instead of us the fans (and ofc much more interested in her take than in some others expressed here, and I mean no disrespect with that). Fans are kind of a conservative bunch -speaking about storytelling- always eager to repeat the same standards and reluctant to anything "new", without realising that almost always that means the possibility of being surprised by the narrative disappears. Always sticking to the tried-and-true (which, btw, flashbacks also are) leaves you with... well, ONLY with the tried and true.
