Local office workloads are highly relevant, which I think would really make SC stats inaccurate. In addition, I think I-751s are a low priority as we are seeing, it seems, more and more N-400 interviews scheduled with pending I-751s. If priorities were equal, I-751s would always be processed prior to N-400s, imo. There are many more N-400 applications than I-751 petitions received by USCIS each quarter according to the stats I have seen.
Example in case as evidence to USCIS priorities:
1. We filed a joint I-751 in March of 2019.
2. Status went to "Case is ready to be scheduled for an interview" in May 2019.
(Crickets)
3. Wife filed N-400 in August 2022.
4. N-400 interview conducted in December 2022. 2 days prior to the N-400 interview, we were notified that it would be a combo N-400/I-751 interview.
We had received no RFEs for either the I-751 or N-400.