I would have thought the Withdrawer to be slightly stronger than a Rook,
but it seems to be the contrary when I pit four Rooks against four
Withdrawers, both in David Howe's Chess on a Longer Board with a few
pieces added on 10x8 and in this game on 10x10. (Rectangular boards such
as 10x8 or 12x8 obviously favor the Rook over Queen-moving types.)
Still, the Withdrawers (and the other pieces) should be more valuable in
these games than in Ultima, because they alone offer baroque capture
(other than en passant) and can easily attack a chain of Pawns.