This.
One of the many things I loved about through time and space was that you could get all the girls without needlessly playing it over and over again.
Especially if you make the cast smaller and focus more on the relationship buidling, only being able to have one relationship per playthrough is going to be maddening. Because if an update happens and your not on that girl's path... you get no update...
It's just always better if you allow an (optional) harem and then people can pick and choose if they only one to see a solo route, good on em, but if people want to see all the routes in a harem route, thats their too.
I don't think it's all that bad, it's not like I'm gonna do one route for each girl and in each of that route, you'll only get that one girl. It's more about the girls at the house and for the relationship to be a bit more meaningful, so the MC isn't at home with a mother and her two daughters and they all just want to have sex with him at once, with no regard for each other.
What I have in mind, and I feel like I'm just repeating myself at this point, is that there will be True romantic relationships with the three main girls, which will contain all the scenes with that girl. If you have that True relationship, the other two girls know about it and you can't have one with them. And then there being sort of secret relationship, more superficial, where you can have multiple of them, but don't have all the scenes. I could see making myself a magic button, which unlocks this and you can have all the relationship, sort of a cheat, but I wouldn't accommodate this with a story, as it wouldn't make all that much sense, without bending the story to make sense of it as I did in TS. If that makes sense.
TL
R I could make a cheat button to unlock all relationship no matter what, but I wouldn't make sense of it with the story and I wouldn't write around it, which could result in some inconsistencies.