Getting good facial recognition has probably more to do with where the camera is being placed in relation to the approach. being at close to eye level, located in a position likely to catch the person looking directly at the camera, and having a long approach toward the camera for a better chance at a good still image between the frames which is in focus. If someone is rounding the corner just before the camera, it will be difficult to get a good shot unless they stand still for a few and stare directly at the cam. If someone ID's the cameras and still makes an attempt they will try to keep their head down after that so you kind of want the camera to be a surprise. You want them to figure out the camera has a great shot after they find the camera. After that you can tweak shutter speed, sharpness, brightness etc etc in any camera. The same holds true with the lens choice. If you can get a zoomed in narrow view of a walkway where the perp is likely to walk through, excellent. But a lot of times when people mount a camera on the wall of the door, they want a wide angle to view the porch for packages and see what the person is doing at the door. Are they trying to turn the handle or force entry? You won't see that without a wide angle and offset from the wall/door. So you will have to choose whether you want the zoom lens or more of a wide angle for the location. Is it more important to see their face, or what they are doing at your door? Or do the zoom lens and then mount another facing the door opposite. I have a Dahua dome with a 2.8 lens and it works great. At night my porch light illuminates the porch well since its partially enclosed, so light reflects everywhere. I don't even need IR for that camera. Environmental variables are just as important as the camera when choosing what will work best. Sometimes you can improve the environment for far less than unloading tons of cash for an expensive camera for the same effect. Something to evaluate. I'm not an installer, some of these ideas are just basic logic.
What was wrong with the Dahuas you purchased out of curiosity? 2 with mechanical problems seems like a high rate.
