Finland has a population of 5.5 million people. They have almost 900 000 soldiers including reserves in their armed forces that they can mobilize in case of war.
When war breaks out, they have already trained as many people as possible. There aren't many left to conscript at that point.
It was the same for Sweden during the cold war. The armed forces would have numbered almost a million soldiers out of a population of 8 million. On top of that, an additional 1.5 million swedes were part of the total defence forces.
> My claim is that on average, the third group will perform more poorly than the second group. I don't mean to compare either to the first group.
The thinking in Sweden has always been that conscription leads to a democratization of the army, stronger popular support for the armed forces, and a stronger will to defend the country.
So sure, if the country is invaded, the people who have not served before and refuse to do so even after an invasion will not be as good soldiers.
It is not 1940 something.
Perhaps the specific example I gave of Finland does not hold, but I think the spirit of my example still does.
First profi army becomes senior force, that trains whomever wants to hold a gun (second army). There is never political support to draft third army (like everyone). Remains of first army flee after government collapses. Political regime changes.
However, I was speaking somewhat more narrowly of active defensive combat situations. I think this is pretty different from the peacetime conscription practiced by Finland, Sweden, etc. I was speaking of the group that did not volunteer when given impetus to do so.
Let's say that Finland were invaded by Russia. First, the currently-conscripted Finnish army would defend. Secondly, any additional volunteers from the populace that would like to help defend their homeland, will also help defend. Thirdly, if these first two groups are insufficient, additional conscription will be performed against the remaining population.
My claim is that on average, the third group will perform more poorly than the second group. I don't mean to compare either to the first group.