They don't want any man having sex with any potential LI (or woman in general) besides the MC. My best advice is to just ignore those complaints.
If it's good and people like it, you'll gain a following.
The issue is the fact that sophia is having sex with anyone at all, except the mc. First impressions count, its as simple as that. I am not a fan of anyone having sex or any form of mutual masturbation with my potential LI ever at all, but that is just me, but then again i am sure that applies to a great number of people who will be exposed to this vn.
My issues with a lot of VN is that they try to cater to far too many people, and they end up not pleasing anyone at all. Ignoring the complaints and simply pretending they don't exist is a recipe for disaster, a big disaster.
The fact that the majority of people will see that sophie is having sex with anyone other than the mc, is really not going to go down well at all, infact this single thing alone at least so far, will be the cause of this vn falling hard on it's ass. Catering to the minority who don't care, well given that the dev will want this to be a success, that won't happen unless some changes to sophie are made from the outset.
There can be various ways to do this without ruining the mc main storyline or the other girls. Make her a side character who is simply unimportant who isn't fucking anyone period. She can be a LI for the mc. I've no idea how you could do that without it looking corny or just forced onto the mc.
You could do a similar thing as above but not a side character, but as one of the main girls, but again she is not fucking anyone, similar to above she can be a LI for mc.
Just like Zoe she could have a crush on the mc, isn't fucking anyone , and there is some kind of rivalry going on between to the two of them for the mc affection. However as dev as said, the girls like to share, which would exclude this possibility altogether since I would run my own harem type thing. That being said, maybe the mc has to use corruption on sophie because she is some stuck up bitch or whatever and may not like the mc very much , until both she and the mc warm up to each other etc, i don't know.
The common theme is that very few people want to see sophia fucking anyone else at all period. If she is, then I will put this thread on ignore and pretend this vn doesn't even exist, because I for one, am not remotely interested in any VN which puts the mc on the sidelines and allows any of his potential LI to be fucking anyone else. It just isn't to my tastes.
Also it goes without saying, a lot of vn fall on their ass before even getting going because of the mc being a manchild, with childish like responses etc. It's okay to be romantic and say romantic things, but there is a clear boundary to saying things that are just out of place or just sound retarded. This is the trap many devs and writers fail in, and the story becomes irrelevant, a well written mc either makes or a breaks a vn from the very start. keep him consistent throughout the story. his personality should be the same from beginning to end. let him have fun etc, but try not to turn him into some manchild.