I just ordered mounted Leve to use as my Emissary for my Leve crew and I was actually being disappointed about the exact same thing
It would have been great to have him on a horse also... with the Riders in tow...
sigh, I'm currently very tempted to just pick up the 4 riders and paint them up just to have all 5 of the riders, maybe I can convince someone to let me play them together just for laughs :p