Unless... fort defense/offense strength scales with the square of strength, so if you can find a way to get your strength drained down to -200 or something (I've had units drained to -40 vs. R'lyeh so this shouldn't be impossible), you should be better at fort-wrecking than Scabiel.
IIRC, according to the manual, flying basically just adds a siegebonus (1).
-Max