Tenjiku Shogi also has no anti-trading rules. But I actually played that, and even after trading away the Fire Demons and neutralizing the danger of the jumping generals it remains an enormously tense game, because you can get back a Fire Demon through promotion. Which creates an immediately winning imbalance. The Water Buffalo's themselves are only average pieces (by Tenjuku standards), and are not easily traded. So equiping some less important pieces with decisive promotions might be an alternative to anti-trading for keeping a large game exciting.
It also helps that both the Fire Demon and Water Buffalo come in pairs, and are both sliders.
It also helps that both the Fire Demon and Water Buffalo come in pairs, and are both sliders.