The chart is made by the same guys who wrote the article, so I'm guessing they didn't run a last check over it. The massive Cube on the chart is the one from TNG, and I suppose by the article the Tactical Cube AND the normal looking Cubes are supposed to be the 1500M ones. They only put the Tactical Cube on the chart.
So, again, all the Borg in VOY were smaller and weaker than from TNG.
Sure, it doesn't matter in the end because the audience was still going to hate that they just used weaker Borg ships, but what can you do with an unpleasable audience?