It is easy to forget how Superman dominated the DC landscape in the early 1960s. Nowadays it is accepted that DC's two biggest stars are Superman and Batman, with not much separating the two in the public's mind.
But back then there is little doubt that Superman was the big star and Batman a B-lister. And it's not all that surprising. Superman had a very popular radio show in the 1940s and an even more popular TV series in the 1950s which was quite commonly shown in reruns, while Batman's crossovers had been limited to guest appearances on Superman's radio program and a couple movie serials in the 1940s.
When you look at the sales of the two characters in the early 1960s, there is no comparison. Seven of the top nine comic titles published in 1962 featured Superman prominently: Superman, Superboy, Lois Lane, Jimmy Olsen, Action, World's Finest and Adventure; the only comics in that grouping that did not include him were Archie and Casper. And even that does not tell the entire story of his dominant position at DC. The figures given for circulation are per issue, here are the annual figures:
Just looking at the two main titles for each character (Superman and Action, Batman and Detective), Supes was outselling Batsy by about 70%. If we look at all the Superman titles except World's Finest and all the Batman titles except WF, Superman was outselling Batman by 4.4 to 1; including WF for each would only reduce that to about 3.3 times. (Note: I don't consider the JLA to be a title for either character; especially in the early days of the Justice League, Batman and Superman were only occasionally featured in that magazine).
If we look at the 1965 circulation figures (DC did not publish numbers in 1963 and 1964), just prior to Batmania, we see a similar story; the top six comics published that year were the core Superman-related titles, followed by Archie, then WF and Batman.
Note in particular that almost all the DC titles showed significant gains in sales between 1962 and 1965, with the exception of Wonder Woman, Mystery in Space and Sea Devils. The latter two titles would be cancelled within the next couple of years, and Wonder Woman was rebooted twice. I suspect that the circulation increases from 1962 reflect demographics, as the biggest bulge of the baby boom reached its prime comics-reading years.
In 1966, of course, things changed dramatically, as the Batman TV show became an overnight sensation. Batman's own title doubled in sales, while Detective showed a 33% jump. The Superman titles all slumped a bit, with declines ranging from about 5% to 13%. The only Superman-related title to jump in 1966 was (not surprisingly) the one he shared with Batman, World's Finest.
Like every fad, Batmania collapsed on itself and by 1969 sales of Batman and Detective had collapsed to their lowest levels of the decade. Unknown to comics fans of the time, changes had taken place that were about to set the stage for one of the greatest eras for the character.