Just as Vladki said.
Obviously, cargo might become more profitable if people were actually able to transport the demand, but I would not call this a change in the underlying economics, rather than fixing issues with the intransit system that prevented the underlying economics from actually working as intended.
Just as the new system you suggested might achieve this.
Anyways, it might simply have been a missunderstanding of what was meant by "changing the economics".
To be honest, I did not even consider the amount of goods a pack horse can carry might be excessive.
However, 1 ton did sound quite a lot, and two units of meat actually are 820kg in case of meat and fish, or 770kg in case of milk, so I did a quick recherche on pack horses.
Most packhorses were Galloways, small, stocky horses named after the Scottish district where they were first bred. Those employed in the lime-carriage trade were known as "limegals".[4] Each pony could carry about 240 pounds (110 kg) in weight, spread between two panniers.
That means it might be sensible to reduce units to represent 100 kg or something like that, so our pack horses can be balanced to carry 100 kg and the resulting higher number of goods (in terms of simunits, not in terms of kg), might already solve the current transport chain issues.
Again, assuming the issue is JIT not behaving well with small numbers.