Borg is 10-5 against Nastase (3-3 on clay).
He made a great season but not the best ever. It is at the same level of Vilas and/or Nadal (considering only clay), being Rafa's probably the best one.
and in '73, Borg was only 17 years old, before Borg became a dominant player.
Vilas probably should have been ranked #1 in '77 (won RG, USO and 14 other titles, was runner up at AO and won 46 consecutive matches), but the ranking system was dumb and gave Connors #1.
Connors streak of 200-something weeks at #1 was, imo, a bogus record, because Vilas should have been #1 in '77.
Ashe was arguably #1 in '75, and it seems like Borg should have been #1 in '76. Borg won Wimbledon without losing a set, won the finals of World Championship Tennis (a big event at the time), and reached the finals of USO.