I have to say the question is indeed interesting, and got me musing about the harem definition and if it applies to this.
However I also think that this series is also considered harem. Even though he (and everyone else) knows who he loves, Keiichi always falls into
situations that "isn't what it looks like".
I know that it's hard to compare AMG with Love Hina. A better comparison would be Ai Yori Aoshi which is also considered harem.
Waitaminute....
If AMG is harem, then Suzuka would also be harem...
Gah, I need to think this out...