If you pay enough attention to details involving hybrids, you'd notice that non-hybrids CAN overwhelm defeat hybrids by themselves (after a brutal beating, which is a given). So far however, only two have done it without foul play: Victor used his combat experience to even out his fight with Michael, and William was in one hell of a feral state, which allowed him to last some time against the same hybrid.
In Selene's case, being frozen in a block of ice for a dozen years straight (don't ask me about childbirth) was enough to dampen her reflexes but she was weaker than Quint was in a full frontal assault. The reasons she managed to kill him was:
1. A grenade lodged into his stomach (It nearly doesn't count)
2. His transformation made him roughly elephant-sized, causing him to have trouble getting into enclosed spaces
3. She had better flexibility than he did due to the size difference
In Blood Wars, she was rendered useless because of a nightshade-rubbed knife, almost killed due to drained blood and thrown around by a transformed idiot who looked like a misshapen gorrilla compared to other transformed Lycans.