It turns out that the fillibuster was created decades later and first used in 1837. Therefore, even if the population is distributed the same, the represented population needed to block legislation is considerably higher. Without a fillibuster, it would take at least 18% of the population to block legislation rather than the aforementioned 11%. Working off the 1790 Decennial Census and combining Maine and Massachusetts and ignoring the fillibuster, it took senators representing 24% of the population to block legislation. Interestingly, it takes senators representing a minimum of 26% of the population to pass legislation in face of a fillibuster which is very close to the 1790 proportion.
Note that some of the difference above is due to the fewer states and the discrete nature of the voting. Below is the cumulative population distribution against the proportion of US Senate representation for 1790 (red) and 2010 (blue). Visually, one can see that the 2010 Senate is more skewed. For kicks, the Gini coefficients for 1790 and 2010 are 39% and 50%, respectively. I'm no historian, so someone else will have to address the question of what the Founding Fathers would think of today's circumstances ... or if what they would think matters. More to the point of the original article, it should be clear that small population states have a much bigger influence in the Senate than in the past obstructing legislation.
|Cumulative Population against Cumulative Senate Representation|
RED: 1790 population
BLUE: 2010 population