I have about 1600 vamps.
Bite cool down is fine. I get periods of great success, and then periods of fails or repulses. its all part of the RNG its not going to look perfect, but it works. Its high risk - you're doing something that is a high risk action. the rewards is awesome, but you're gonna get a stiff penalty if it fails. This is one reason I love vampires - entirely unpredictable. Its great to be able to turn cool codes into a cool vampire. Also the same note the AH dangit! when it fails. If I recall success is 50% fail is 50% (divided into 25% repulse and 25% kill) And when I am doing a lot of biting, that is what I see.
I take high risk by taking rare eggs with gorgeous lineages and turning them into beautiful vampires. I do not see the point in making them easy-peasy - they should not be.