Most of the radiation released was NOT point source, concentrated material. It was tritium. The water circulated through the cores to cool them did indeed contain a lot of concentrated material (bits of the core, irradiated material from the damaged buildings.) That was removed by filtering. If all that happens is a lot of tritium gets released - then it will have about the impact of a lost truckload of car batteries. Some potential risk if the worst happens (i.e. all the batteries crack open and end up in a water reservoir) but not catastrophic. (BTW the lead in car batteries is one of the most recycled materials in the world. I was thinking more of the cobalt in li-ion batteries, which are not recycled or tracked in any way.)
As a percentage of the total release, which was large, maybe. As an absolute amount, it was a bad scene. Worst since Chernobyl. The cores melted, and released on their own as well. And then? Too late for that to be all.
Unfortunately the real story about the historical and future consequences of this incredible disaster will probably never be made public, due to the significant investment globally in nuclear energy. Also not enough is known about how increased background radiation levels effect human dna and other health disorders. We have a reasonable understanding of short term affects but little knowledge of long term affects (generational). The incentive to keep a tight lid on it all is very high, high enough to be extremely skeptical of published media and other managed info sources. IMO