The assertion that Batman was obviously not better than the Spirit was made in the comments-section here.
I hesitate to invoke the Theory of Modes so soon after writing BUFFY THE MYTHOS SLAYER, which essay, to those not versed in Fryean categories may, seem a little like walking in on the part of HAMLET where Polonius says:
"The best actors in the world, either for tragedy, comedy, history, pastoral, pastoral-comical, historical-pastoral, tragical-historical, tragical-comical-historical-pastoral, scene individable, or poem unlimited. (Hamlet, II, 2: 392-396)"
I could well understand it, then, if a reader found it difficult to follow both the four narrative *mythoi* I derived (with only slight changes) from Frye (comedy, drama, adventure/romance, and irony) plus the four underlying myth-themes (my word), anagnorisis, pathos, agon, and sparagmos). I can perhaps best explain them by saying that they are all phases through which writers conceive the "power of action" given to fictional characters within their fictional world, and that though a writer may borrow storytelling elements from any of the categories the telos (narrative purpose) of each story generally hews to one division more than to any others. Each category has validity in itself and none is inherently inferior to another (contrary to an opinion expressed by Theodor Adorno, to the effect that great literature was defined by "negativity": in Fryean terms, irony a la Kafka).
In the BUFFY essay I mentioned that it wouldn't be hard to conceive of the show as a "drama with adventure-elements," though I demonstrated why I felt that there was a better case for the opposite: "adventure-with-drama-elements." In comparing BATMAN and THE SPIRIT, though, I am dealing with two works that I deem both fall dominantly into the category of the adventure-mythos. Also, I consider both of them to be "superheroes" (though I'm currently working on a better critical term for the narrative typologies they share).
It is certainly possible, within the exemplars of a given mode, to say "X is great but Y sucks." The modal theory is not made to excuse incompetence, but to spell out how different creative modes succeed in different ways. Thus, if a work falls dominantly into the adventure-genre, then it stands or falls as to how good a job the creators do in evoking the thrill of the agon. In that respect I find the two subjects on equal ground, even when comparing Eisner's SPIRIT (which pretty much lasted the length of the Golden Age before its cancellation) only to BATMAN comics of the corresponding time period.
HOWEVER, one *can* fairly argue, though, that purely in their evocation of certain *subsidiary* elements, SPIRIT was better than BATMAN or BATMAN than SPIRIT.
For instance, of the two SPIRIT is far better than BATMAN in evoking elements of pathos. On the whole BATMAN scripts of the Golden Age are better-constructed melodramas than most other costumed-crusader stories of the time (see my remarks about Jerry Siegel's writing here), but Eisner and his collaborators are clearly better dramatists than any of the Bat-creators. Some, though not all, of the credit goes to the visual style Will Eisner pioneered for the strip, which could be used as easily for serious drama as for rough-and-ready action. By contrast, though BATMAN of the Golden Age had its share of moody visuals, those visuals generally served only the purpose of heightening the action-sequences.
On the other hand, because BATMAN is more of a "pure adventure" concept, and so is more divorced from consensual reality, BATMAN is much stronger than the SPIRIT in terms of evoking mythopoeic fantasies. As much as I am attracted to the pathetic elements of SPIRIT, I find relatively few of the stories possess the element of mythicity. That's why, when I made up my "Library of Mythopoeic Comics," I only selected a particular exemplar of symbolic complexity, the "Jimson Weed" tale, rather than including the whole gamut of SPIRIT-stories.
And while it's true that there are many BATMAN-tales that don't reach that level of complexity either, dominantly the BATMAN feature became a place where popular myths could thrive and grow. Some of them became widely famous through adaptation into other media, like Joker and Catwoman, and some remained confined to obscurer parts of the Bat-mythos, but the process that allowed such characters to grow symbolically was not duplicated by Will Eisner, whose focus was more upon "ordinary people" rather than extraordinary supercriminals.
(I've noted here that "ordinary people" can in theory be as "symbolically complex" as the more outrageous creations of fantasy, but one still has to bring to those ordinary people a sheen of the extraordinary within the ordinary--which I don't think Eisner did.)
Naturally, for anyone minded to judge Eisner's SPIRIT to be a pure drama, there would be no point in comparing it to an adventure-opus like BATMAN, as the primary myth-themes of each would be too divergent.