Koans the hallmark of Dogen's Zen?

[In China at the time Dogen visited] All public monasteries, whether or not their abbacies were reserved for Ch’an monks, had basically the same buildings, bureaucratic structures, schedules of activities, and basic forms of Buddhist discipline and practice. All public monasteries had buddha halls (butsuden), where various offerings and sutra chanting services were held; dharma halls (hattō), where abbots gave lectures and entertained questions; and sangha halls (sōdō), where the main body of monks sat in meditation, ate, and slept at their places on the open platforms. If there was anything that was distinctive about the Ch’an monasteries, it was not the stress on zazen or the occasional ritual in which the entire community was required to perform manual labor together (fushin samu) — those practices were common to all the public monasteries. No, what distinguished the training in Ch’an monasteries was chiefly the teaching style of the abbots, who based their talks and debates on the koan literature that was the hallmark of the Ch’an tradition.
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To summarize, what the so-called transmission of Zen to Japan in the thirteenth century really amounted to was the wholesale transmission from Sung China of the latest in Buddhist monastic institutions, teachings, and practices.
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The Zen school in Japan, or rather the various Zen schools (plural) that were based on branch lineages, were institutionally separate from the other schools of Japanese Buddhism...
Nevertheless, they were heirs not only to the Chinese Ch’an tradition of dharma lineages and koan study, but to the entire Buddhist monastic tradition as it flourished in Sung China.

Dogen himself stressed in the chapter of his Shobogenzo entitled “The Buddha Way” (Butsudō) that what he was transmitting was not just the “Zen lineage” (zenshū) — a name that he castigated — but true Buddhism in its entirety. At the same time, he boldly asserted that his own line of dharma transmission, passed down through his teacher Ju-ching, preserved the true Buddhism better than any other line.
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It is true that Soto teachers gained prestige from their membership in the Zen lineage, and that to become a member one had to master the tradition of commenting on koans.
~T. Griffith Foulk, History of the Soto Zen School

Peace,
Ted