Ghandi was not poor. He was a trained lawyer with experience working abroad who adopted some practices in solidarity with people who were actually suffering in poverty. Just because he wasn't a millionaire doesn't mean that he hadn't accrued significant social capital, and the influence over economic capital that this represented. His capacity for good was rooted in this dual capital access; he did not necessarily have a similar capacity for evil, because social capital is not fungible in the same way that economic capital is.
But without either form of capital, one's reach is commensurately shortened, so no, such a poor person does not have the same capability to "cause a lot of suffering" as someone who is rich.
>As the number of poor persons is bigger than the number of rich people, the accumulated potential for good or evil they have, adding their individual evil or good, is probably bigger than the good or evil potential of rich people
Astonishingly, wealth inequality has ballooned to the point that the holdings of the top percent or so so dwarf that of the rest of the planet that it overcomes the population disparity.