The best sandbox, with zero grind is still a VN with unnecessary extra clicks. Which is faster, click door to exit your room, click entrance hallway, click door to exit house, click Character A location on the map, or have a choice on screen with 'go to a date with character A'(one click) to get to the exact same content?
There is zero benefit in trying to game-fy a renpy 'game', no matter the effort it still plays like shit compared to Unreal Engine and the likes and multiple negatives, extra code that increases the chance to get fucked up and cause bugs, less players because they filter out your game by that tag, you get my point.
You want bonus content, have it accessible from the main menu as side stories, you want to have optional dialogue, use the Witcher 3 system of colored text for main story and white text for extra lore.
If we stop pretending, devs go for sandbox/free roam because it gives them extra excuses for longer dev cycles. Change my mind!