Usually a 'better' antenna means one with more gain.
Which means one that is more directional.
Which means less sensitive in some areas in exchange for more sensitive in others.

Less sensitive in some areas might not be better for a collision avoidance.
Perhaps you could focus more on a pancake at you altitude.
Maybe a longer vertical dipole would do this.

Instead of a dipole made of 2 back to back 1/4 wave elements,
I wonder how 2 back to back 5/8 or 1 1/4 wave elements would do?

Also, the WiFi folks seem to have settled on a coaxial configuration for the dipole. This fixes the problem of the feed getting in the way of the elements. I'm not sure if it affects the pattern from underneath.