Balancing a pub is impossible unless policed religiously by humans. At which point it would just be annoying. You cannot balance players skills. Specifically because many CS:S players play fantastic sometimes and horrible others. You simply cannot know how well someone is going to play (except in certain situations such as the elite players and the very very bad players). The problem can’t be solved by this or anything else we do, just play the game and win or lose, have fun regardless. I’ve seen teams balanced as much on our server as I have on other servers with no balancing configurations/plugins.
Unless you have some way to telling the future or an extremely effective probability calculator, then you will not balance teams.
Also, teams can still be stacked with Auto Join. All Auto Join will do is make the stack unintentional (maybe).