The Flying Dragon move that also appears in Dai makes sense. It would be odd for the Bishop to appear in Heian Dai without the Rook as well. In fact, I can't recall any other game that has that property.
In Ten Shogi Variants by George Hodges, he says that Maruo Manabe made up the moves for the pieces and that influenced Steve Evans to put the moves in the image above:
The late Maruo Manabe, of Chigasaki, Japan, who during the 1970s and 1980s was widely considered to be the foremost expert on the Shogi variants, studied this problem of the possible moves and promotions of the pieces. Giving credence to later texts and theories, he suggested moves for those pieces not met with in normal Shogi for those who might wish to try out the game. He assumed that all pieces promote to a Gold General at the
third rank, except for the Flying Dragon, which adds the power to go one step in the four orthogonal directions. (Bishop becomes a Dragon King)
You're more informed than I am about the dates of things. Wish it were possible to ask the designers of the games about their thought processes and their choices. Oh well.
Also, Tomoyuki Takami posted his thoughts on the game in 2015 (in Japanese) and believes that it was made before Dai, though with the pieces closer together. He's done extensive research on other variants like Maka Dai Dai as well.
The Flying Dragon move that also appears in Dai makes sense. It would be odd for the Bishop to appear in Heian Dai without the Rook as well. In fact, I can't recall any other game that has that property.
In Ten Shogi Variants by George Hodges, he says that Maruo Manabe made up the moves for the pieces and that influenced Steve Evans to put the moves in the image above:
The late Maruo Manabe, of Chigasaki, Japan, who during the 1970s and 1980s was widely considered to be the foremost expert on the Shogi variants, studied this problem of the possible moves and promotions of the pieces. Giving credence to later texts and theories, he suggested moves for those pieces not met with in normal Shogi for those who might wish to try out the game. He assumed that all pieces promote to a Gold General at the third rank, except for the Flying Dragon, which adds the power to go one step in the four orthogonal directions. (Bishop becomes a Dragon King)
You're more informed than I am about the dates of things. Wish it were possible to ask the designers of the games about their thought processes and their choices. Oh well.
Also, Tomoyuki Takami posted his thoughts on the game in 2015 (in Japanese) and believes that it was made before Dai, though with the pieces closer together. He's done extensive research on other variants like Maka Dai Dai as well.