I was thinking about having a short-range burning piece, which burns diagonally adjacent pieces, like what the Fire Dragon does in Minjiku Shogi. This creates the desired power gap while still allowing adequete defense against the power piece, even without jumping sliders. An example is shown below.
My only reservation is that introducing any form of burning makes it more a Tenjiku-Shogi variant than a Dai-Shogi variant. If it was up to me I would prefer to only use moves of a type that are already in Dai Shogi. A quite strong piece without solo-mating capability could be made by enhancing a Queen with linear two-leg moves like exist on the Horned Falcon and Soaring Eagle.
My only reservation is that introducing any form of burning makes it more a Tenjiku-Shogi variant than a Dai-Shogi variant. If it was up to me I would prefer to only use moves of a type that are already in Dai Shogi. A quite strong piece without solo-mating capability could be made by enhancing a Queen with linear two-leg moves like exist on the Horned Falcon and Soaring Eagle.