For me, a perfect harem would be where the protagonist doesn't pick girls like cabbages and accepts them easily. Personality and relationship are really important. The protagonist just can't save the person then the person just fell in love with him. Afterall, for me saving a person just added some good will against the protagonist however that actually isn't an actual reason for the protagonist and the harem member to be together. Just point out how they fell in love and how they got in love to the point that sharing their lover is okay. I think a perfect harem party is actually limited to 7 just not double digits because I think it will crumble the harem. (My opinion though) I also think that having a girl/boy who actually despise sharing their lover to others, broke their relationship and ended up single alone/ married to another is quite interesting. Like if their relationship isn't that strong or not as strong as the protagonist and other's relationship, I would actually think this is quite interesting. (My opinion) To be fair, I usually avoid some harem tags because of how badly they are written. I read some harem like World Apocalypse Online and I liked it in my book.