P-G: Your first point. GrandChess is 10 squared board but don't lose from sight it is only one more than Shogi (9x9). I imagine such promotion could tears the opponent front.

I think the argument that the Shogi general isn't effective in GrandChess hasn't so much to do with the board size, as well with the other pieces. In Shogi, there are only 4 pieces that have a long range: rook, bishop (and their promoted pieces), and the two lances. But the lances can only move forwards, and cannot deviate from their file. In Grand chess each side has 2 rooks, 2 bishops, a queen, a marshall and a cardinal. In (grand)chess, on average, the pieces have a far greater mobility than in shogi. Picking a piece from shogi, and dropping it into a chess variant is usually not going to work. Chess, shogi and Chinese chess aren't games with just a set of pieces randomly thrown together. No, chess, shogi and Chinese chess work well (and are hence popular) because of the combination of pieces work well.

It's like taking a unit of Napolean's army that worked well for him, and putting it in the German army of 1940. It ain't going to work.