McGonagall, Slughorn, and Shacklebolt were able to square off against Voldemort.
The Potters survived Voldemort 3 times.
Moody and Bones did it a few times too.
Lord Voldemort canon was scary against people who didn't fight, but against resistance, he doesn't fare well enough to be able to justify what he's doing. Being held off by 3 Hogwarts Professors means you are not cut out for taking on all the Aurors Magical Britain can spare unless Hogwarts Professors are worth half a dozen Aurors apiece.
And in real life, Physics Professors are not worth half a dozen soldiers armed with weapons built out of physics.
I'm not sure how to justify Hogwarts Professors being super good in fights, but yeah, something just tells me that if Teachers are better than Police Officers, then your society is really really screwed and anyone with half a brain is going to look like.....well, like a wizard.
After Book 4 suggested a new way for Harry to be special (Brother Wand Effect), that view of Harry being special was immediately dashed when the Death Eaters were trounced by 5 out of the 30-odd memebers of Dumbledore's Army. OK so the kids were scared and they were trying as hard as they could and they barely got out with their lives and Hermione and Ron did get hurt...but none of them died, not against Lucius Malfoy, Bellatrix Lestrange, Antonin Dolohov, and half a dozen others. These were the best Voldemort had. These guys should have been like Nazgul. Should have been able to kill children and hide the bodies.
Clearly nobody in canon HP uses Avada Kedavra as much as they use other spells because they.....because they.....are afraid of Azkaban and think they can get off on practically anything but an Unforgiveable? No that doesn't seem right, you can blame it on the Devil Imperiused Me To Do It....so...what then? Why don't Death Eaters kill as much as it's made out they do?
I really don't know.