Unable to reproduce the performance difference between ArcGIS Pro and ArcMap (BG64). Similar average times between the two apps using the same machine for testing.
Use the PairwiseBuffer_analysis tool in ArcGIS Pro. It runs in parallel and is a bit faster for many cases.
The following are outputs from testing:
Buffer_analysis:
ArcMap 10.x BG64: 21s
ArcGIS Pro: 21s
PairwiseBuffer_analysis:
ArcMap 10.x BG64: n/a
ArcGIS Pro: 7s