As mentioned in the other thread, ocean plastics have nothing to do with landfill-disposed trash. They're mostly fishing nets waste, and at that, mostly from mismanagement by a handful of poor countries.
I'll assume good faith here and that you were simply unaware of the origins of the so-called great garbage patch, but in future discussions I think it would do your arguments some credence not to bring up ocean plastics in response to discussion about landfills.