It sounds like you are saying that you have an existing notion of what the spell is supposed to do, and you are interpreting the wording in light of that notion. I would ask where your existing notion comes from, but we have been down that road and it seems to go nowhere useful.
Perhaps here we can point to the 2e spell, which I think was the first version. It includes the line "It can bear the weight of the creature it was created for, plus 10 lbs per caster level." That tilts heavily toward your interpretation.
I suppose also the spell name also leans against serving as a draft animal, since "steed" is pretty much used for a horse carrying a rider.