MESD can only pump what ends up in the ditch.
Today there are still areas of the community served by old style combined sewers that will only pump down when the Wastewater Treatment Plant catches up with the demand. Only then will the water be out of basements. In other words...these customers drain through the sanitary sewer system, not through Nameoki Ditch.
The handy political narrative is that MESD created this problem. A 9 inch rain in 4 hours created a problem akin to a 250 year flood for systems that just aren't engineered to handle them.
Today I was in an elderly ladies house whom was pumping her sump pump furiously into the sanitary sewer system. Not good. If the sewer system is already full, that same water runs into their neighbors basement but now it's mixed with sewage! They all connect together, and go to the treatment plant, not to Nameoki Ditch.