I've been at assemblies at which one person was baptized. So let's do the math:
You said 1300 were there. Now let's allow for an average hours/month per publisher of 5, despite the fact that they encourage 10 hours per month. We'll give them the benefit of the doubt and say 5.
1300 x 5 = 6,500
Now, since there are two assemblies per year (plus the convention) and it takes around six months to study with someone to the point where they become a Witness (assuming this person was found door-to-door and was not born-in), we mulitply the 6,500 by 6:
6,500 x 6 =39,000
So that's 39,000 hours of Field Service to produce one JW. Not very efficient.
If the person was born-in and just took forever to get baptized, then those 39,000 hour produced 0 JWs.