I'm not yielding to your premise but I'll entertain it for a moment. Massive biological differences aside, the rough composition and weight of a deer isn't so much different than a human. An AR chambered in something like 6.5 is one of the most ergonomic and effective deer killing machines you could possibly use. Very light, able to make follow up shots easily, swappable magazines, insane aftermarket availability and cheap ammunition for training because nearly the entire US military uses the parts, etc etc.
can you back this up with how many hunters prefer going out with handguns as their weapon of choice for hunting deer?
I mean, I've not heard any of the hunters I know complaining about the efficacy of their hunting rifles for taking down deer, moose, or even bears.
How many deer are you trying to kill in one go??