Per https://en.wikipedia.org/wiki/Celebratory_gunfire, a bullet traveling at 200 feet per second can penetrate human skin. So even terminal velocity is significant and can injure or kill.

The reason perfectly vertical bullets are less dangerous is that they tumble and this tumbling reduces the terminal velocity below dangerous levels. Presumably tumbling could also happen at lower angles due to wind or other factors, it just is less likely.

It takes considerably more to kill someone than to break the skin. Maybe if you are laying on your back and the falling bullet hits the carotid artery, but this is a really contrived example.