one doesn’t need any more... if they intend on only shooting a dozen deer. Or if they intend on having perfect form on every shot they take, out of their perfectly tuned bow, so that every arrow flies perfectly true without any side loading, And of course without ever clipping any leaf or twig on the way to the target. And if they intend on hitting within 2-3” horizontally of where they aim every time - and the deer, which can move 12” forward backwards up or down in the time it takes your arrow to get there, decides to play along and stay still.
I think over several millennia countless thousands of native Americans who killed countless 10s of thousands of 1Klb+ American bison with basic longbows using wooden shaft arrows tipped with flint arrowheads might just give you a valid counter argument.
For the record I have successfully killed 43-46 whitetail deer (yes I have kinda lost count of the numbers of doe I've killed) in 37 years of bow hunting 22 were bucks admittedly mostly were 2 year old bucks. And I do not see how cleanly killing 10, 20 or hundred deer differ from 10 in terms of proving anything as long as all or as in my case 99+% were clean quick kills with short under 100 yards tracking and recoveries. Only two went farther than 100 yards and I still recovered them. So far I have hit and failed to recover only two deer. The first one I literally still have no idea what the h#!! happened. I shot and as far as i could tell nothing unusual happened to the arrow in flight, deer never reacted till after being hit, no strange noises no wild odd arrow flight just released the arrow, the familiar smacking noise of hitting a deer and deer ran off. 22-23 yard standing still broadside shot. Found my XX78 AL arrow intact but bent. Shot was towards end of shooting light. At the hit buck took off like he fully lit his afterburners never really had a buck I arrowed react quite so violently before or since that I can recall. I was honestly quite startled. Arrow had blood all over it. Was VERY early in my deer hunting career and was my 11th deer a averaged sized 6 point. Positive it was only muscle blood on arrow. Spent three days looking never found him.
Sulked a very very long time about that one. Having gone 10 for 10 in my first four years of bow hunting on making well placed shots and fast recoveries most I heard or saw go down gave me a false sense of infallibility. Only other deer I hit and lost is to long a story suffice to say I screwed up wore heavy insulated one piece I never practiced in that my bow string hit the breast pocket at release and my ineptitude caused my poor hit and never found that buck. Again no evidence of a lung, liver or stomach hit just muscle blood. In both instances no matter how heavy an arrow I used wouldn't have made a wooden nickels worth of difference as both arrows went all the way through the deer.
You want to shoot 600-700 grain arrows and 1.5-2" fixed blade BH's by all means do so. It certainly wont diminish your killing effectiveness. But I don't see how it's at all needed to kill a deer. I mean how dead do you need dead to be? We all know killing deer begins and ends with shot placement. Shot placement is what kills deer or any animal for that matter. Put a razor sharp BH through both a deer's lungs and your odds of quickly recovering it are 99% in my experience.