I don't "failed to comprehend".
full 64 slot server. Your idea:
"German players begin to quit. Only let newly arriving people join the German side. If the Germans still continue to lose, only add new players to the German side until they win or they have 6 to 8 people more than the other team"
so if 10 people drop from the axis team and the server has 10 more slots to fill, how could they outnumber the allied team at any point? I doubt mostly nobody will drop (from allies) when his team is steamrolling (and if, the amount would be too small - and please don't bring stuff from other Threads in this discussion).
Workable solution? If you see that the enemy team gets screwed and you are a good player? Join them and motivate some of your team members to do the same. I don't think a lot of people will actually do it but it's still better than overloading a server with 72 slots (which is not possible - atleast that's what I think, because there are no high slot servers)