Claims about disproportional representation are almost always based on presidential election results, ignoring the midterm elections, even though the midterms are equally important for the Senate.

The 2014 election shouldn't be ignored, because it explains why Garland wasn't confirmed and Trump's appointments were. That year, Republicans won the popular vote by a margin of almost 6%, and won 9 seats in the Senate.

That election gave them control of the Senate until 2020, and that outcome was representative of the popular vote.

https://en.wikipedia.org/wiki/2014_United_States_elections