Can you explain what you mean with this rhetorical question?

The short answer is no.

The long answer is the whole of history

I’m not sure that a deep understanding of slavery and freedom on that level is possible for those of us fortunate enough to be born in a time and place without widespread open slavery. I’m not sure why an activist today needs to be an expert on that subject in the same way, unless you’re talking about historians or other academics.

Probably not, and taking your rhetorical question in its best possible light, the difficulty in learning the history of activism as it pertains to black folks is far harder than I think most take it to be. You're not just fighting "whatever is causing people to be less interested in history," you're additionally fighting the part of white supremacy that has consistently and actively pushed confusion and misinformation.

Yes.

Is there anything specific you have in mind that Smith had which ‘modern race activists’ don’t?

Smith certainly seems extraordinary but that Douglass remark seems to be (at least in isolation) rather unclear—what sort of ‘understanding’ is meant here? And presumably Smith stood out amongst his contemporaries too, so neither ‘modern race activists’ nor nineteenth-century ‘race’ (or other) activists would in general be as talented as he was.