Which is why it might make sense to combine it with glucose lowering agents. I think your intuition is absolutely correct - it will take a combination of interventions to hit PD, furthermore, because PD is so heterogenous, it might take different combinations depending on the individual patient.
We can divide this into two parts. One is the triggering etiology, and the other into repair of the damage, similar to prevention vs cure. If the original insult is limited to the inciting incident, then all you are addressing are the downstream effects, like in the example where a drug destroyed substantia nigra leading to a PD presentation. What can you do about etiology here other than stopping the damaging drug, focus on recovery. But when PD is a progressive disease, with an underlying pathology, you must focus on addressing that too, otherwise you’re just addressing symptoms, like focusing just on dopamine. So, if say, pesticides cause PD, then how does this PD progress? Presumably, you have exposure, then the exposure stops - so why should PD keep progressing after the exposure stops? But if there is some other underlying pathology that keeps the PD getting worse over time, I guess that’s the target. Circling back to the original issue - what exactly causes PD, and what caused your particular PD, that might determine how to address it. And to gain clues as to the cause, one should at least keep vigilant track of as many relevant biomarkers and symptoms as possible, and based on that try to figure out the particular presentation that might indicate where exactly is the problem and how to tackle it.