This is something that really separates Borg and Connors in '78. They ran close in total number of (official) titles, and in total number of losses. But Borg won 2 Slams to Connors' 1.Borg did also win Roland Garros, against Tanner,Ramirez,Barazutti and Vilas and lost no sets in the process...
It's true that World Team Tennis had diminished the strength of the RG field since '74; but in '78 there were fewer absences of top players at RG than at any time since WTT began. Six of the Top 20 were missing at RG -- the same number that were missing at Wimbledon.
I think RG in '78 actually came out slightly ahead of Wimbledon in an evaluation conducted by WCT (the criteria were strength of field and prize money); someone made a post about this a year or two ago.