I think you maybe arguing with someone else. They made a straight forward claim that is incorrect:
> If we are only looking at the federal level, then there has been no substantial reduction.
There _was_ a significant reduction at the federal level. They acknowledged that and then changed the goalpost.
I then claimed
> Studies on this topic are fraught because the gun industry has long prevented the normal research funding issues on this topic and have fought tooth and nail any data collection efforts.
This is true. The Dickey Amendment prevented first the CDC and then the NIH from collecting gun violence statistics from 1996 until today. Though in 2018 they were able to add a rider to it to make it a little easier.
FOPA makes it impossible to collect registration information for federal use, including in data exchange for studies around gun ownership.
I'm not sure what more you want me to backup. Would you like the actual legal citations on those?