i disagree, making it a sandbox would help the game alot. i think you are confusing bad sandbox games. that either dont make use of its gameplay, or force terrible grinding.
Like i said already, to me, it would fix the problem with the amount of girls, as it would give each of them a better pacing. and a road to develop them(and the story).
and i highly doubt the game would be worse than it already is. with this directionless, kinetic novel just keep the button held to progress.
While I dislike sandboxes, I freely admit that it is because most of them are bad.
The thing is though - sandboxes mostly aren't that story heavy - which WVM wants to be.
If it succeeds is subjective, but for one coherent story, a sandbox used to separate the girls and progress them independently does not help at all.
And then - if all those girls were independent of each other, each of them would be an island - combining them would be much more difficult. Not impossible, but it would contradict the idea of separating them to be able to develop them without strings attached.
And if I hate anything more than (bad) sandboxes, it is a (non) story, that just is 5 stories in one, where you pursue '5' completely isolated girls, and they never even meet.
Also, while there were slivers of an approach to only lewd a select few girls in the beginning (where you had to answer in school which girls you wanted to pursue), that's not a viable option anymore - imagine a cast of 50+ girls (and growing, rapidly!!), where you had to render each variation of LIs. Just putting them all in your harem is much better to handle (if there were actual content handling them ...).