I agree that Lendl's RG title (when he beat the Italian Open champion Gomez in quarters, and the 1982 champion and 1983 finalist Wilander in the semis before overcoming Mac) has been downplayed here. 'If not for his RG win' is not a good arguement at all. He did win it, and thus that achievement was far more significant than anything that Connors achieved all year. Both players were very consistent throughout the whole year, regularly reaching the latter stages of tournaments big or small, but Lendl also had a very important title win where he beat the dominant player in the world in the final.
Connors failed to win any of the blue chip events in 1984 and had a terrible record overall against his 3 main rivals that year, with losing records against all of them. Not a very strong case for being the second best player of the year at all, against a player with a blue chip title win and a more respectable record against the big guns.
Even in non-official/invitational tournaments which were important back then, Lendl's body of work was probably better than Connors's in 1984 as well, with him winning the European Champions' Challenge in Antwerp for the second time plus a couple of other events.