I think Jarls with their "stomping boots" on can do real damage to calvalry....
Really, if Boots of the Behemoth work, that's the way to go.
I think the size is ok. When I was playing in SP I had to fight EA Van as EA Argatha. Rather than lay down and die, I instituted a mass breeding program for trollgytes. They killed the EA Van so badly I almost thought I was cheating. Just pac-manned them up. No contest.
I thought trampled units always took one point of damage?
__________________ In strait places gar keep all store,
And burn the plain land them before:
Then shall they pass away in haste,
When that they find nothing but waste...
I thought they still take a point if they make the def check, blowing their glamour?
Not so useful against equipped Van thugs. But still nice.
If they are being used in large numbers, countering with one Neifel Jarl with trample boots would help drop the glamour. And a bunch of others to actually do damage.
Probably better to just try for area affect attacks.
You might try the swarm spell. Low level low cost nature. It is a surprisingly nasty little spell. I use this spell a lot of times in the arena and have brought down powerful pretenders with it.