Part of the problem with waste management is that we don't really put it in the soil. Your household garbage is mostly biodegradable, but if it ends up buried in a lined pit under tons of other garbage, even paper and orange peels will probably sit there for centuries. I'm not sure it makes much of a difference what kinds or quantities of plastic end up buried in the landfill.
I think the solutions here are more on the supply side than the landfill side. The question there is what are we trying to solve.
Energy use? Most alternative packaging materials are energy-intensive too, so it's less about plastic and more about retail and consumer preferences to have everything individually wrapped and packaged in bags or boxes with colorful graphics, nutrition information, and so on.
Environmental pollution? There, the problem is the plastic that doesn't end up in a landfill. Including our "recycling" shipped overseas.