Quick google search shows articles citing "30,000 backlog" of people wanting appointments to cancel.
You can buy a gun in 15 minutes at a gun store normally. Want to put a suppressor on it or that gun just happens to be 1" shorter than 16"? You're going to wait 9-24 months longer. Ridiculous doesn't even begin to describe it.
The problem is that government is so large that, in practice, the ATF doesn't care, because that $200 just goes into the US Treasury general fund. If they actually kept most of the tax they collect, I think we'd see much faster processing times, and eFile would have happened many years ago.