A 0-0 game can never be finished until someone puts a run on the board. Your logic isn't sound.
Even a team full of replacement level players is going to score runs. Not many, but they will. If you have a team full of Adam Dunn's, who can hit but can't field, you're not going to end well. Likewise, if you have a team of Darwin Barney's, you're also not going to bode well. My point is that you can't go with the extremes, but if you're somewhere in the middle of the spectrum, I don't think it makes as big of a deal.
Since 2010, when Castro entered the league. Tulo has been the only SS who has been worth over 30 runs with his bat in a season, and that is this year. Zobrist(is he even a SS?) and Reyes each had a season where they were worth 29 and 28 respectively. So my example of 30 runs with the bat was poor.
If you can get 10 runs with the bat out of your SS, he's likely going to be right at the top.
On defense, Simmons has the anomaly in that last year he was worth 24 runs. The next closest has been JJ Hardy in 2012 with 12. If you're worth 10 runs with your glove at SS, you're going to be right at the top too.
A SS who is worth 10 and 10, is going to come out to be about a 5 WAR player. It's actually kind of hard to come out with a negative on defense, given the 7.5 boost for position(which I had not really included in the runs listed above, this is just the overall look).
As long as you're okay at defense at SS and have a good bat, you're going to be alright. So I guess you're right, the bat is more important.