What this fails to address is the primary reduction cycles that nature applies to anything entering the ocean.
The first of those is temporary stranding on the sea shore. Why this is important is that storm action activates the seashore to become what is effectively a natural ball mill. Everything gets ground down and turned into sand sized material at the least. It takes time, but also even that is measured over a few seasons. That is precisely why no archeology survives at this interface.
What is not reduced this way may escape temporarily into the open sea and there stay afloat until accretion carries it down to the sea bottom to be trapped by sedimentation. Thus it is no surprise to find plastic particulate in the middle of the ocean and not so much floating debris. The surprise is the particulate itself.
After that the second agency is oxidation of the plastic itself. Most plastic has lost significant integrity after twenty or so years as any householder knows. At some point it is completely broken down. That we are not finding plastic older than forty years should reassure us.
It is all still unsightly and yes we need to intercept it all. Better yet, if we cannot make a plastic that decays quickly for common use, perhaps we need to make a plastic that oxidizes smoothly and much quicker than we presently accept. That mean dating all plastics with a best by date and then perhaps allowing only a decade. The stuff is cheap enough to support this and the manufacturers will even be happy.
Most produced plastic is intercepted and either incinerated or placed in a landfill. Improving the oxidization cycle is helpful here as well. Again, a century from now it will all have largely disappeared.
Where Does All the Plastic Go?