I think kurumu is so much ahead of moka since while moka is just a damstell in distress kurumu saved her plus tsukune countless times , if kurumu wasnt there tsukune would probably be a ghoul . Lets also not forget ruby who saved tsukune from his first ghoul transformation etc...
The way i see it moka is the least deserving girl but tsukune favors her what can you do
anyway i dont want tsukune to dump kurumu and be happy with moka , a small harem with 3 or people may just be fine wo knows .