We are pulling a '79 Boler
with our Forester and are being very careful to keep the Boler weight
below 1500lb--with electric brakes
The only difference we can find between the Forester and the Subaru Outback, which has a higher towing capacity, is that the Outback has larger brake rotors. This suggests that stopping, not towing, is the limitation.
I agree with the comment - do your research.