The black is called soot , but weather it is harmless or functions as fine grinding compound is unknown.
It is not an unknown to oil companies and engine builders. When I first got into the heavy equipment business in the 1960s oil analysis, soot particle size, dispersants, soot clumping etc were much in focus for DD and Cat. The oil companies were quite successful in joint collaboration with the engine builders to extend both rebuild dates and oil changeout intervals. Not only was soot a marker, but another dozen or so "items" as well.
Filtration improvements, engine design, better fuel, oil analysis programs and smart operators all played a role. Improvements continue. Sales, costs, warranties and equipment uptime are measurable and competition is fierce.
Advances in on equipment monitors, computer controls and maintenance detailing have today's industrial engines running longer, increased oil change intervals and generating more continuos HP per CC than just a few decades ago.
Doubtful any of this is relevant to our little low use recreational engines though. Change oil and filters regularly, sure use some bypass techniques but remember soot dispersant decreases as your oil ages. If you're lucky enough to have a commercial rated engine, treat it to fresh oil and it will last a very long time internally.
But then for that pesky sea water side -----