Presumably the mount can still serve as monster bait and trap detector even if falling weight is outlawed?i must confess guilt in doing this myself in early 3e. I had a wizard PC who would use the mount spell to drop a horse on foes. Roof wrecker, falling weight, monster bait, trap detector and other exceedingly cruel applications of the mount spell had the DM at the time name the mount summoned 'Agony'.
Be nice if the rules had a bit of guidance about "the steed serves willingly and well". I think I'll rule that it serves willingly and well only as a mount. For anything else, if you could get a real horse to do it (possibly requring a Handle Animal check) then you can try and get the mount to do it.
