I agree that the Connors-Mac age difference is an issue w/r/t h2h (similar to the Connors-Lendl age difference, which is equivalent to Fed-Nishikori in terms of the age gap). That said, I think you can cull some meaningful data from approx. 1979-1983 for Connors/Mac, to the extent both guys were winning slams during that period. Great, dramatic encounters between the two at Wimbledon, the Open, Dallas, Philly, Wembley etc. during these years.
And I think you underrate Connors-Borg, which was the heavyweight championship rivalry in tennis for at least 3, and arguably 4 years in the late 1970s (1976-79 by my count). Basically, in addition to level of play (which was often high between these two, their GS title fights in 1978 notwithstanding), you've gotta account for the stakes of the rivalry, including multiple Wimbledon and Open finals, plus finals at big ticket events like Philadelphia, the YEC, and the Pepsi Grand Slam during these years.
From their US Pro Indoor final in 1976 through their raucous RR match at the YEC in 1979 (when the torch was truly passed to Borg-McEnroe as the preeminent rivalry), Connors-Borg was at the heart of a rapidly growing sport. Hell, I saw a rerun of "Magnum, PI" a few weeks back from early 1981 where Higgins tells Magnum that the two are staying on the grounds of the estate that weekend, so he can't use the tennis court.
Just about all of their encounters were title fights during this era as well. Basically, the importance of this rivalry can't be understated.
Anyway, Borg-Mac is probably my favorite as well from a tennis perspective - I just wish it lasted longer. Same with Lendl-Mac, which seems to've really only stood out above all other rivalries from part of 1984 through 1985 (it arguably shared the bill with Mac-Connors and Connors-Lendl from 1982-84, similar to the current "big 3/big 4" era since about 2011/12). Wish Mac hadn't taken his Hollywood detour in '86, would've loved to see how an engaged J.P. McEnroe would've handled the emergence of Becker at Wimbledon and Lendl everywhere else.