Another consideration for the long rotation is that FFG regularly releases a mechanic/keyword on a only a few cards in a set. This sometimes takes over a year for them to release enough cards in supplemental packs to make the keyword/mechanic viable. If the rotation went too fast you may never see some of these cards even be that viable.
That said, I am not sure how this will work for L5R, where in the past, the story drove numerous card decisions (such as the death of a character). AEG, after their initial, no cards banned, no cards restricted era, cycled cards fairly quickly, too quickly for me. I am not a fan of the rapid rotation of new cards like MtG.