Hmmm....I took 2 small, Tennessee deer to processors in 2009; my first hunting season in the states.
I got less than 80lb of meat total, from those deer. The back straps were the size of my arm when I took the deer in, but I got less than 10lb of steaks back. The rear hams were cut with a bandsaw & basically ruined. I never got any neck or rib meat at all. Total 'stew' meat was under 30 & I got 22lb of ground.
From 2 whole deer, I got less than 70lb of meat back.
Since then, I've worked at 2 other processors & I understand how they work a little better. Time = money & believe me, they're not cutting into every nook & cranny....if a cut has a lot of sinew/fat/membrane? Shitcan.
Butchering efficiently & proficiently takes time & patience & they're the 2 things game processors don't have at the height of hunting season. I've been cutting all my own, plus deer & hogs for a few select friends since 2010. Not for money (all i ask is a pack of vacuum bags per deer) but mostly because I really enjoy that aspect of the whole field-freezer thing. They come to me because I'm thorough. Not quick, probably not the best cutter, but because if they bring me a gutted carcass weighing 200lb, they know they'll be getting a minimum of 80lb back.
But.....to get that percentage (bearing in mind I've got all the time in the world & working on one carcass at a time.....) it's going to take me 4-6hrs.
Learning to butcher cleanly & efficiently, if not quickly, is one of the best things I've invested my time in.
When I hunt out west, I'm prepared & happy to devote at least 3 days of/after my hunt just to butchering & packing my meat. Shipping yourself is silly spendy, but absolutely worth it.