Of the 2 million plus men who served in Vietnam more than half were either combat soldiers, close combat support or in areas subject to regular attack.
But let’s go with your 10% number. The Vietnam draft was a vehicle to replace infantry troops. The Navy and AirForce had no problems filling slots.
So if you draft about 300,000 per year as we did during the height of Vietnam what do you do with 150,000 18 year old girls per year who want nothing to do with being GI Jane?
You really need to compare that to all the people who served in the military during the Vietnam war, not just those in the war zone. Millions served inside the USA, and other bases around the world during that time. But I'm against the draft in general because it's bad for the military, and an unnecessary attack on individual liberty. It also makes fighting wars more politically unpopular, which is why some Democrats love the idea. They also love the idea that the government has the right to conscript citizens for the military and non-military service. IMHO there should have to be a direct threat to the survival of the country with a DOW before we resort to it. I guess we could always put those women down on the border.