In the early 2000s B-52s carry a huge number of unguided gravity bombs but a strike fighter using JDAMS was more effective with only few bombs.
It's not how much ordnance an aircraft carries, it's about how much of it actually hits the target.
The questions to ask is just how accurate are the F-35s guns going to be and why does the F-35 require such sophisticated fire control software.
The gun would seem to be there to support ground troops (missiles for dogfights). The A-10 likely performs the ground support mission in better fashion.
Another question would be if the F-35 has the legs and maintainability to be there when needed. I simply do not see a great deal of value in the 400 billion and counting, spent on this solution to many problems. There is a very high likely hood that it will continue to under deliver.