Considering that plant based powders were the highest in Lead, and there was that whole thing with Cacao last year, and before that with Spinach - I wonder if vegetables might have higher sources of heavy metals.

But then, I wonder why that would be, and how effective can washing them well be? I assume the high heavy metal sources also mean the soil is contaminated and therefore things grown in it too are.

The 20/80 rule probably applies. 20% of effort for 80% result, the rest isn't worth chasing.