PERF: regression in datetimelike symmetric_difference set op
This seems to have caused several performance regressions, see https://pandas.pydata.org/speed/pandas/#regressions?sort=1&dir=desc (the ones for commit "bf72b70b")

_Originally posted by @jorisvandenbossche in https://github.com/pandas-dev/pandas/issues/41833#issuecomment-858560156_