It sounds like one solution to this would be having the entire party enter turn-based mode, with members either being in or out of combat. It seems like that would be a very easy change to make, because turn-based mode can already trigger automatically, but the question would be how well that all blends together while you’re playing. I think that should be tied to difficulty; in Story you can cheese like you do now, while in hardcore (or whatever it’s called) you always enter turn-based.
I this is partly the consequence of adapting a tabletop system to a video game. In DND your DM obviously wouldn’t pause combat indefinitely while the rest of the party messes around, but a DM can account for out-of-combat shenanigans much better than a game that must use pre-defined systems.
Actually in my current run (on Balanced) I’ve found that I can’t really do that. If I group sneak towards enemies I can attack with one of my characters, they leave hiding to make the attack, and then typically get spotted and start combat (unless it’s from far enough away that they can re-hide and attack again before the target gets within sight). Then all the involved characters roll initiative, and my character that attacked doesn’t have an action for that turn. Any other members of my party that are hidden can still attack out of combat, but the same situation occurs; they leave hiding to make the attack, get spotted, roll initiative, and then when their turn comes around they don’t have an action (haven’t had the chance to see how this works with extra attack). This could probably be cheesed with super favourable terrain and some pre-planning, but I think at that point you’ve more or less set up an ambush and it’s ok to get some extra benefit out of that.
IMO this is a pretty good way to handle it within a video game context, because it limits the cheese while not totally removing player agency by possibly undoing your attack. Like you said it’s different to how that’s handled in tabletop, but as a DM I’m able to explain how initiative is literally a skill check to see how quick on the draw you are, so my players hopefully don’t feel as cheated if they want to attack first but can’t act before the enemy. I do enjoy how the player urge to get as many free attacks in as possible at the start of combat is the same in both games hahaha.