Molasses is mostly sugar (sucrose) with some extra minerals; iron, calcium, and potassium being the ones probably of most interest to cannabis growers.
The sugar, bluntly, is a disaccharide that the plants roots can't absorb, and it does nothing for the plant.
On the other hand, adding sugar to the soil is a great way (in my opinion) to attract insects and other pests. Hurray! It probably does improve the flavor of the soil. Yum!!
The minerals might help, if the growing soil/medium were short on those. As mentioned above, molasses can act as a chelator, potentially locking up certain minerals, though I don't think this effect would that pronounced with only small amounts diluted with water.
I won't exclude that adding sugars could feed bacteria in the soil that might help fix nutrients, though its not clear to me why trying this would be preferable to adding necessary nutrients in a controlled manner via a properly formulated fertilizer/nutrient mix.
I think its just as likely that you're going to cause fermentation by yeasts in the soil, potentially altering its pH and inhibiting growth.
In short, in my opinion the thesis that molasses adds nothing is correct.