Bad villain? Yes. Wuss? No.

1. "obsessed with mother"

There is debate whether Sephy he is controlling Jenova, or that Jenova is controlling him. Either way, it still doesn't make him a wuss, because he would either be trying to obtain the power of Lifestream for himself and not "mother" (even though he does say he wants the planet for mother a few times) or if Jenova was controlling him, you still can't say he is a wuss because it is not him. After all, it would be Jenova because he/she/it would be controlling Sephy.

2. "cuts his mom's head off"

It wasn't Jenova's head. If you're talking about the flashback with Cloud, Sephy removes the mask off of Jenova's containment chamer, not her head. Yeah, it was the only way he could see Jenova.

3. "gets beat by Cloud"

Well duh, the heroes always beat the villains.

4. "tries to kill Tifa and hitting girls is wussy like"

Hitting and killing are different. A murderer killing somebody who happens to be a girl is way different from some boy punching or picking a fight specifically with a girl.

5. "kills Aerith/Aeris from behind"

Haven't you heard of murderers who shoot/stab/kill somebody from behind? Almost all murderers attack from behind, since if the person saw the killer coming, they could run away and/or make it difficult for the murderer to kill them.

Oh and one final thing I would like to point out...
The "actual" Sephiroth is the one that you see in Cloud's flashback, the one that was sealed in the Northern Crater. The Sephiroth that you see for most of the game is acutally Jenova.