You can also look at surface achievements. Borg was undefeated in '78 on clay: 20-0 in official matches. As Kiki mentioned, he won RG without the loss of a set (and with the fewest ever games lost).
Borg was also undefeated on grass (though his only grass event was Wimbledon).
Connors lost matches on all the surfaces: hard, carpet, grass and clay.
On the other hand Connors won titles on all those surfaces, while Borg failed to win a title on hardcourt (losing in 3 events).
Best hardcourt player of the year was clearly Connors (3 titles, 1 loss).
Best on clay and grass was Borg.
Each man won 4 titles on carpet.
No large margin here for either man. The differences that stand out are Borg's extra Slam title; Borg's large lead in non-sanctioned events, some of which were considered important at the time even if they're off the radar today; and Borg's significant edge in H2H against the rest of the field.