There is the chemist's way of approaching the problem, which is to see if there is a specific compound (i.e. juglone) that is responsible for the allelopathy. That leads to isolating the compound, seeing if it can be synthesized in the lab, and that leads to seeing how it can be modified, studying how modifying the molecule changes the allelopathic properties, the molecular mechanism of action, etc.
But other sciences have their own way of approaching the problem. The chemist's way is how people come up with the idea of making synthetic herbicides like glyphosate, which opens the Pandora's box of unintended consequences. The problem with the more natural way that you refer to is that it requires a whole lot more data than we collectively have at our disposal. It's a lot more expedient, not to mention more profitable for a chemical manufacturing company, to cook up mass quantities of a specific molecule than it is to know which plant to prescribe as the natural cure.
This is a little off the topic of allelopathy, but I should relate my story about using a natural cure yesterday. My neighbor has some eggplants that don't look so well. Knowing that we have some
Fusarium problems with the soil in the neighborhood, I made up a root drench of mustard leaves and
compost tea and gave them a good drenching. We'll wait and see if that perks them up a bit.