Bergeron and Kopitar had pretty equal offensive ability, the only real difference in their yearly point totals was utilization and PP time.
For their careers, they have basically identical ES PPG at 0.52 for Bergeron (666 in 1,294) and 0.55 for Kopitar (796 in 1,439). The difference is Bergeron in his prime averaged 45% o-zone starts to Kopitar's 55% o-zone starts and Kopitar had an extra 1 to 1:30 a year in PP time.
And Kopitar may have been physically bigger, but he didn't play bigger averaging under 50 hits and 30 PIM a season