Before proceeding to more questions regarding percevied issues of "legitimacy" within the BATMAN comics franchise, a quick sketch of the first four "ages of the Dark Knight" seems appropriate, to show in capsule-fashion how the franchise changed over the years in creative terms.
I'll christen the ages as follows:
(1) THE FEVER-DREAM AGE: The first year of Batman's adventures in his initial two titles may have started out with a swipe from a SHADOW pulp-tale, but most of the stories read more like THE SPIDER than THE SHADOW. During this short-lived, pre-Robin period, the artists favored lots of chiaroscuro effects and physical grotesquerie, and the plots leaped madly from one weird subject to another, from killer clowns to vampires to mad scientists to devil-men who turn people into flowers.
(2) THE DICK TRACY AGE. In or around the introduction of Robin, stories took a more ratiocinative, procedural feel. Grotesquerie still appeared, notably with the 1942 introduction of Two-Face, but now it was subsumed by plots that were more nominally more logical, rather than simply lurching from one wild battle to another. Artist Dick Sprang did not work on Batman until 1943, but for fans of the feature Sprang's design-sense has become synonymous with this age.
(3) THE WARM AND FUZZY AGE. In 1955, the producers of the Batman franchise, headed by editor Jack Schiff, took the first step in imitating the more successful Superman franchise captained by editor Mort Weisinger. In June 1955 Batman and Robin acquired the recurring character of "Ace the Bat-Hound," very possible in response to the introduction of Krypto in ADVENTURE COMICS #210 that March.
Some further additions to the "Batman Family" of the period actually predated any one-on-one comparable figures in the Superman Family, in that 1956's "Batwoman" predated the introduction of recurring character Supergirl in 1959.
However, it should be pointed out that Superman had encounter distaff versions of himself prior to 1956; they simply had never been intended as recurring or series-based characters, as with this 1951 super-powered version of Lois Lane.
Though Dick Sprang continued to contribute to the Batman features into the early 1960s, the artist most associated with the franchise in the early Silver Age was Sheldon Moldoff. Even in 1955, Moldoff can be seen trying to retain the hard edge of Sprang's line. However, by 1956 one can see Moldoff's line becoming more "warm and fuzzy" in that characters have a more rounded aspect. Indeed Big Name Fan Mike Tiefenbacher, former editor of THE COMIC READER, once commented that in this period Batman began to look rather chubby-cheeked, like the Legion's Bouncing Boy
Stories from this period became somewhat more antic, as Schiff endeavored to build up Batman's repertoire of costumed villains. However, the period has become better known among Batman fans for the introduction of the impish Bat-Mite, a clear derivation from Superman's spritely villain Mxyzptlk, and for the introduction of many contrived alien menaces. Possibly the editor had some idea of taking advantage of a moderate science fiction in comics of the late 1950s, but it should be said-- as I pointed out here-- that Mort Weisinger was also pursuing a similar strategy at the time.
(4) THE NEW LOOK AGE: Imps, aliens and the old members of the Batman Family all got the heave-ho in 1964, when editor Julius Scwhartz took over the Batman features and instituted the first overtly heralded change in the Batman family: what the cover of DETECTIVE COMICS #327 called "the New Look." In BATTLE FOR BAT-LEGITIMACY PT. 3 I'll deal with the ways in which the changeover was announced and some ways in which readers reacted, but for now I'll conclude by referencing, for anyone interested, this essay as to what was different about the "New Look."